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data-event-name="pinnable-header.vector-toc.pin">move to sidebar</button> <button class="vector-pinnable-header-toggle-button vector-pinnable-header-unpin-button" data-event-name="pinnable-header.vector-toc.unpin">hide</button> </div> <ul class="vector-toc-contents" id="mw-panel-toc-list"> <li id="toc-mw-content-text" class="vector-toc-list-item vector-toc-level-1"> <a href="#" class="vector-toc-link"> <div class="vector-toc-text">(Top)</div> </a> </li> <li id="toc-Relation_with_the_Gregorian_calendar" class="vector-toc-list-item vector-toc-level-1 vector-toc-list-item-expanded"> <a class="vector-toc-link" href="#Relation_with_the_Gregorian_calendar"> <div class="vector-toc-text"> <span class="vector-toc-numb">1</span> <span>Relation with the Gregorian calendar</span> </div> </a> <button aria-controls="toc-Relation_with_the_Gregorian_calendar-sublist" class="cdx-button cdx-button--weight-quiet cdx-button--icon-only vector-toc-toggle"> <span class="vector-icon mw-ui-icon-wikimedia-expand"></span> <span>Toggle Relation with the Gregorian calendar subsection</span> </button> <ul id="toc-Relation_with_the_Gregorian_calendar-sublist" class="vector-toc-list"> <li id="toc-First_week" class="vector-toc-list-item vector-toc-level-2"> <a class="vector-toc-link" href="#First_week"> <div class="vector-toc-text"> <span class="vector-toc-numb">1.1</span> <span>First week</span> </div> </a> <ul id="toc-First_week-sublist" class="vector-toc-list"> </ul> </li> <li id="toc-Last_week" class="vector-toc-list-item vector-toc-level-2"> <a class="vector-toc-link" href="#Last_week"> <div class="vector-toc-text"> <span class="vector-toc-numb">1.2</span> <span>Last week</span> </div> </a> <ul id="toc-Last_week-sublist" class="vector-toc-list"> </ul> </li> <li id="toc-Weeks_per_year" class="vector-toc-list-item vector-toc-level-2"> <a class="vector-toc-link" href="#Weeks_per_year"> <div class="vector-toc-text"> <span class="vector-toc-numb">1.3</span> <span>Weeks per year</span> </div> </a> <ul id="toc-Weeks_per_year-sublist" class="vector-toc-list"> </ul> </li> <li id="toc-Weeks_per_month" class="vector-toc-list-item vector-toc-level-2"> <a class="vector-toc-link" href="#Weeks_per_month"> <div class="vector-toc-text"> <span class="vector-toc-numb">1.4</span> <span>Weeks per month</span> </div> </a> <ul id="toc-Weeks_per_month-sublist" class="vector-toc-list"> </ul> </li> <li id="toc-Dates_with_fixed_week_number" class="vector-toc-list-item vector-toc-level-2"> <a class="vector-toc-link" href="#Dates_with_fixed_week_number"> <div class="vector-toc-text"> <span class="vector-toc-numb">1.5</span> <span>Dates with fixed week number</span> </div> </a> <ul id="toc-Dates_with_fixed_week_number-sublist" class="vector-toc-list"> </ul> </li> <li id="toc-Equal_weeks" class="vector-toc-list-item vector-toc-level-2"> <a class="vector-toc-link" href="#Equal_weeks"> <div class="vector-toc-text"> <span class="vector-toc-numb">1.6</span> <span>Equal weeks</span> </div> </a> <ul id="toc-Equal_weeks-sublist" class="vector-toc-list"> </ul> </li> </ul> </li> <li id="toc-Advantages" class="vector-toc-list-item vector-toc-level-1 vector-toc-list-item-expanded"> <a class="vector-toc-link" href="#Advantages"> <div class="vector-toc-text"> <span class="vector-toc-numb">2</span> <span>Advantages</span> </div> </a> <ul id="toc-Advantages-sublist" class="vector-toc-list"> </ul> </li> <li id="toc-Differences_to_other_calendars" class="vector-toc-list-item vector-toc-level-1 vector-toc-list-item-expanded"> <a class="vector-toc-link" href="#Differences_to_other_calendars"> <div class="vector-toc-text"> <span class="vector-toc-numb">3</span> <span>Differences to other calendars</span> </div> </a> <ul id="toc-Differences_to_other_calendars-sublist" class="vector-toc-list"> </ul> </li> <li id="toc-Algorithms" class="vector-toc-list-item vector-toc-level-1 vector-toc-list-item-expanded"> <a class="vector-toc-link" href="#Algorithms"> <div class="vector-toc-text"> <span class="vector-toc-numb">4</span> <span>Algorithms</span> </div> </a> <button aria-controls="toc-Algorithms-sublist" class="cdx-button cdx-button--weight-quiet cdx-button--icon-only vector-toc-toggle"> <span class="vector-icon mw-ui-icon-wikimedia-expand"></span> <span>Toggle Algorithms subsection</span> </button> <ul id="toc-Algorithms-sublist" class="vector-toc-list"> <li id="toc-Calculating_the_week_number_from_an_ordinal_date" class="vector-toc-list-item vector-toc-level-2"> <a class="vector-toc-link" href="#Calculating_the_week_number_from_an_ordinal_date"> <div class="vector-toc-text"> <span class="vector-toc-numb">4.1</span> <span>Calculating the week number from an ordinal date</span> </div> </a> <ul id="toc-Calculating_the_week_number_from_an_ordinal_date-sublist" class="vector-toc-list"> </ul> </li> <li id="toc-Calculating_the_week_number_from_a_month_and_day_of_the_month" class="vector-toc-list-item vector-toc-level-2"> <a class="vector-toc-link" href="#Calculating_the_week_number_from_a_month_and_day_of_the_month"> <div class="vector-toc-text"> <span class="vector-toc-numb">4.2</span> <span>Calculating the week number from a month and day of the month</span> </div> </a> <ul id="toc-Calculating_the_week_number_from_a_month_and_day_of_the_month-sublist" class="vector-toc-list"> </ul> </li> <li id="toc-Calculating_an_ordinal_or_month_date_from_a_week_date" class="vector-toc-list-item vector-toc-level-2"> <a class="vector-toc-link" href="#Calculating_an_ordinal_or_month_date_from_a_week_date"> <div class="vector-toc-text"> <span class="vector-toc-numb">4.3</span> <span>Calculating an ordinal or month date from a week date</span> </div> </a> <ul id="toc-Calculating_an_ordinal_or_month_date_from_a_week_date-sublist" class="vector-toc-list"> </ul> </li> </ul> </li> <li id="toc-Other_week_numbering_systems" class="vector-toc-list-item vector-toc-level-1 vector-toc-list-item-expanded"> <a class="vector-toc-link" href="#Other_week_numbering_systems"> <div class="vector-toc-text"> <span class="vector-toc-numb">5</span> <span>Other week numbering systems</span> </div> </a> <ul id="toc-Other_week_numbering_systems-sublist" class="vector-toc-list"> </ul> </li> <li id="toc-References" class="vector-toc-list-item vector-toc-level-1 vector-toc-list-item-expanded"> <a class="vector-toc-link" href="#References"> <div class="vector-toc-text"> <span class="vector-toc-numb">6</span> <span>References</span> </div> </a> <ul id="toc-References-sublist" class="vector-toc-list"> </ul> </li> <li id="toc-External_links" class="vector-toc-list-item vector-toc-level-1 vector-toc-list-item-expanded"> <a class="vector-toc-link" href="#External_links"> <div class="vector-toc-text"> <span class="vector-toc-numb">7</span> <span>External links</span> </div> </a> <ul id="toc-External_links-sublist" class="vector-toc-list"> </ul> </li> </ul> </div> </div> </nav> </div> </div> <div class="mw-content-container"> <main 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class="vector-unpinned-container"> </div> </div> </div> </nav> <h1 id="firstHeading" class="firstHeading mw-first-heading"><span class="mw-page-title-main">ISO week date</span></h1> <div id="p-lang-btn" class="vector-dropdown mw-portlet mw-portlet-lang" > <input type="checkbox" id="p-lang-btn-checkbox" role="button" aria-haspopup="true" data-event-name="ui.dropdown-p-lang-btn" class="vector-dropdown-checkbox mw-interlanguage-selector" aria-label="Go to an article in another language. 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href="https://fr.wikipedia.org/wiki/Num%C3%A9rotation_ISO_des_semaines" title="Numérotation ISO des semaines – French" lang="fr" hreflang="fr" data-title="Numérotation ISO des semaines" data-language-autonym="Français" data-language-local-name="French" class="interlanguage-link-target"><span>Français</span></a></li><li class="interlanguage-link interwiki-nl mw-list-item"><a href="https://nl.wikipedia.org/wiki/Weeknummer" title="Weeknummer – Dutch" lang="nl" hreflang="nl" data-title="Weeknummer" data-language-autonym="Nederlands" data-language-local-name="Dutch" class="interlanguage-link-target"><span>Nederlands</span></a></li><li class="interlanguage-link interwiki-no mw-list-item"><a href="https://no.wikipedia.org/wiki/Ukenummer" title="Ukenummer – Norwegian Bokmål" lang="nb" hreflang="nb" data-title="Ukenummer" data-language-autonym="Norsk bokmål" data-language-local-name="Norwegian Bokmål" class="interlanguage-link-target"><span>Norsk bokmål</span></a></li><li class="interlanguage-link interwiki-ro mw-list-item"><a href="https://ro.wikipedia.org/wiki/S%C4%83pt%C4%83m%C3%A2na_ISO" title="Săptămâna ISO – Romanian" lang="ro" hreflang="ro" data-title="Săptămâna ISO" data-language-autonym="Română" data-language-local-name="Romanian" class="interlanguage-link-target"><span>Română</span></a></li><li class="interlanguage-link interwiki-sr mw-list-item"><a href="https://sr.wikipedia.org/wiki/ISO_%D1%81%D0%B5%D0%B4%D0%BC%D0%B8%D1%87%D0%BD%D0%B8_%D0%B4%D0%B0%D1%82%D1%83%D0%BC" title="ISO седмични датум – Serbian" lang="sr" hreflang="sr" data-title="ISO седмични датум" data-language-autonym="Српски / srpski" data-language-local-name="Serbian" class="interlanguage-link-target"><span>Српски / srpski</span></a></li><li class="interlanguage-link interwiki-sh mw-list-item"><a href="https://sh.wikipedia.org/wiki/ISO_sedmi%C4%8Dni_datum" title="ISO sedmični datum – Serbo-Croatian" lang="sh" hreflang="sh" data-title="ISO sedmični datum" 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.hatnote{font-style:italic}.mw-parser-output div.hatnote{padding-left:1.6em;margin-bottom:0.5em}.mw-parser-output .hatnote i{font-style:normal}.mw-parser-output .hatnote+link+.hatnote{margin-top:-0.5em}@media print{body.ns-0 .mw-parser-output .hatnote{display:none!important}}</style><div role="note" class="hatnote navigation-not-searchable">"Week date" redirects here. Not to be confused with <a href="/wiki/Week" title="Week">Week</a>, <a href="/wiki/Week-day_names" class="mw-redirect" title="Week-day names">Week-day names</a>, or <a href="/wiki/Week_number" class="mw-redirect" title="Week number">Week number</a>.</div> <style data-mw-deduplicate="TemplateStyles:r1251242444">.mw-parser-output .ambox{border:1px solid #a2a9b1;border-left:10px solid #36c;background-color:#fbfbfb;box-sizing:border-box}.mw-parser-output .ambox+link+.ambox,.mw-parser-output .ambox+link+style+.ambox,.mw-parser-output .ambox+link+link+.ambox,.mw-parser-output .ambox+.mw-empty-elt+link+.ambox,.mw-parser-output .ambox+.mw-empty-elt+link+style+.ambox,.mw-parser-output .ambox+.mw-empty-elt+link+link+.ambox{margin-top:-1px}html body.mediawiki .mw-parser-output .ambox.mbox-small-left{margin:4px 1em 4px 0;overflow:hidden;width:238px;border-collapse:collapse;font-size:88%;line-height:1.25em}.mw-parser-output .ambox-speedy{border-left:10px solid #b32424;background-color:#fee7e6}.mw-parser-output .ambox-delete{border-left:10px solid #b32424}.mw-parser-output .ambox-content{border-left:10px solid #f28500}.mw-parser-output .ambox-style{border-left:10px solid #fc3}.mw-parser-output .ambox-move{border-left:10px solid #9932cc}.mw-parser-output .ambox-protection{border-left:10px solid #a2a9b1}.mw-parser-output .ambox .mbox-text{border:none;padding:0.25em 0.5em;width:100%}.mw-parser-output .ambox .mbox-image{border:none;padding:2px 0 2px 0.5em;text-align:center}.mw-parser-output .ambox .mbox-imageright{border:none;padding:2px 0.5em 2px 0;text-align:center}.mw-parser-output .ambox .mbox-empty-cell{border:none;padding:0;width:1px}.mw-parser-output .ambox .mbox-image-div{width:52px}@media(min-width:720px){.mw-parser-output .ambox{margin:0 10%}}@media print{body.ns-0 .mw-parser-output .ambox{display:none!important}}</style><table class="box-More_citations_needed plainlinks metadata ambox ambox-content ambox-Refimprove" role="presentation"><tbody><tr><td class="mbox-image"><div class="mbox-image-div"><span typeof="mw:File"><a href="/wiki/File:Question_book-new.svg" class="mw-file-description"><img alt="" src="//upload.wikimedia.org/wikipedia/en/thumb/9/99/Question_book-new.svg/50px-Question_book-new.svg.png" decoding="async" width="50" height="39" class="mw-file-element" srcset="//upload.wikimedia.org/wikipedia/en/thumb/9/99/Question_book-new.svg/75px-Question_book-new.svg.png 1.5x, //upload.wikimedia.org/wikipedia/en/thumb/9/99/Question_book-new.svg/100px-Question_book-new.svg.png 2x" data-file-width="512" data-file-height="399" /></a></span></div></td><td class="mbox-text"><div class="mbox-text-span">This article <b>needs additional citations for <a href="/wiki/Wikipedia:Verifiability" title="Wikipedia:Verifiability">verification</a></b>.<span class="hide-when-compact"> Relevant discussion may be found on the <a href="/wiki/Talk:ISO_week_date#More_citations_needed" title="Talk:ISO week date">talk page</a>. Please help <a href="/wiki/Special:EditPage/ISO_week_date" title="Special:EditPage/ISO week date">improve this article</a> by <a href="/wiki/Help:Referencing_for_beginners" title="Help:Referencing for beginners">adding citations to reliable sources</a>. Unsourced material may be challenged and removed.<br /><small><span class="plainlinks"><i>Find sources:</i> <a rel="nofollow" class="external text" href="https://www.google.com/search?as_eq=wikipedia&q=%22ISO+week+date%22">"ISO week date"</a> – <a rel="nofollow" class="external text" href="https://www.google.com/search?tbm=nws&q=%22ISO+week+date%22+-wikipedia&tbs=ar:1">news</a> <b>·</b> <a rel="nofollow" class="external text" href="https://www.google.com/search?&q=%22ISO+week+date%22&tbs=bkt:s&tbm=bks">newspapers</a> <b>·</b> <a rel="nofollow" class="external text" href="https://www.google.com/search?tbs=bks:1&q=%22ISO+week+date%22+-wikipedia">books</a> <b>·</b> <a rel="nofollow" class="external text" href="https://scholar.google.com/scholar?q=%22ISO+week+date%22">scholar</a> <b>·</b> <a rel="nofollow" class="external text" href="https://www.jstor.org/action/doBasicSearch?Query=%22ISO+week+date%22&acc=on&wc=on">JSTOR</a></span></small></span> <span class="date-container"><i>(<span class="date">March 2020</span>)</i></span><span class="hide-when-compact"><i> (<small><a href="/wiki/Help:Maintenance_template_removal" title="Help:Maintenance template removal">Learn how and when to remove this message</a></small>)</i></span></div></td></tr></tbody></table> <style data-mw-deduplicate="TemplateStyles:r1257001546">.mw-parser-output .infobox-subbox{padding:0;border:none;margin:-3px;width:auto;min-width:100%;font-size:100%;clear:none;float:none;background-color:transparent}.mw-parser-output .infobox-3cols-child{margin:auto}.mw-parser-output .infobox .navbar{font-size:100%}@media screen{html.skin-theme-clientpref-night .mw-parser-output .infobox-full-data:not(.notheme)>div:not(.notheme)[style]{background:#1f1f23!important;color:#f8f9fa}}@media screen and (prefers-color-scheme:dark){html.skin-theme-clientpref-os .mw-parser-output .infobox-full-data:not(.notheme) div:not(.notheme){background:#1f1f23!important;color:#f8f9fa}}@media(min-width:640px){body.skin--responsive .mw-parser-output .infobox-table{display:table!important}body.skin--responsive .mw-parser-output .infobox-table>caption{display:table-caption!important}body.skin--responsive .mw-parser-output .infobox-table>tbody{display:table-row-group}body.skin--responsive .mw-parser-output .infobox-table tr{display:table-row!important}body.skin--responsive .mw-parser-output .infobox-table th,body.skin--responsive .mw-parser-output .infobox-table td{padding-left:inherit;padding-right:inherit}}</style><table class="infobox"><caption class="infobox-title">Current week expressed according to ISO 8601 <small>[<span class="noprint plainlinks purgelink"><a class="external text" href="https://en.wikipedia.org/w/index.php?title=ISO_week_date&action=purge"><span title="Purge this page">refresh</span></a></span>]</small></caption><tbody><tr><th scope="row" class="infobox-label"><a href="/wiki/ISO_8601" title="ISO 8601">Date</a></th><td class="infobox-data"><span class="bday dtstart updated">2024-11-27</span></td></tr><tr><th scope="row" class="infobox-label">Week</th><td class="infobox-data">2024-W48</td></tr><tr><th scope="row" class="infobox-label">Week with weekday</th><td class="infobox-data">2024-W48-3</td></tr></tbody></table> <p>The <b>ISO week date</b> system is effectively a <a href="/wiki/Leap_week_calendar" title="Leap week calendar">leap week calendar</a> system that is part of the <a href="/wiki/ISO_8601" title="ISO 8601">ISO 8601</a> date and time standard issued by the <a href="/wiki/International_Organization_for_Standardization" title="International Organization for Standardization">International Organization for Standardization</a> (ISO) since 1988 (last revised in 2019) and, before that, it was defined in ISO (R) 2015 since 1971. It is used (mainly) in <a href="/wiki/Government" title="Government">government</a> and <a href="/wiki/Business" title="Business">business</a> for <a href="/wiki/Fiscal_year" title="Fiscal year">fiscal years</a>, as well as in timekeeping. This was previously known as "Industrial date coding". The system specifies a <i>week year</i> atop the <a href="/wiki/Gregorian_calendar" title="Gregorian calendar">Gregorian calendar</a> by defining a notation for ordinal weeks of the year. </p><p>The Gregorian <a href="/wiki/Leap_cycle" class="mw-redirect" title="Leap cycle">leap cycle</a>, which has 97 leap days spread across 400 years, contains a whole number of weeks (<span class="nowrap"><span data-sort-value="7004208710000000000♠"></span>20<span style="margin-left:.25em;">871</span></span>). In every cycle there are 71 years with an additional 53rd week (corresponding to the Gregorian years that contain 53 Thursdays). An average year is exactly 52.1775 weeks long; months (<style data-mw-deduplicate="TemplateStyles:r1154941027">.mw-parser-output .frac{white-space:nowrap}.mw-parser-output .frac .num,.mw-parser-output .frac .den{font-size:80%;line-height:0;vertical-align:super}.mw-parser-output .frac .den{vertical-align:sub}.mw-parser-output .sr-only{border:0;clip:rect(0,0,0,0);clip-path:polygon(0px 0px,0px 0px,0px 0px);height:1px;margin:-1px;overflow:hidden;padding:0;position:absolute;width:1px}</style><span class="frac"><span class="num">1</span>⁄<span class="den">12</span></span> year) average at exactly 4.348125 weeks/month. </p><p>An <b>ISO week-numbering year</b> (also called <i>ISO year</i> informally) has 52 or 53 full weeks. That is 364 or 371 days instead of the usual 365 or 366 days. These 53-week years occur on all years that have Thursday as 1 January and on leap years that start on Wednesday. The extra week is sometimes referred to as a <i><a href="/wiki/Leap_week" class="mw-redirect" title="Leap week">leap week</a></i>, although ISO 8601 does not use this term. </p><p>Weeks start with Monday and end on Sunday. Each week's year is the Gregorian year in which the Thursday falls. The first week of the year, hence, always <a class="mw-selflink-fragment" href="#First_week">contains 4 January</a>. ISO week <a href="/wiki/Year_numbering" class="mw-redirect" title="Year numbering">year numbering</a> therefore usually deviates by 1 from the Gregorian for some days close to 1 January. </p> <table class="wikitable floatright" style="max-width: 50%;"> <caption>Examples of contemporary dates around New Year's Day </caption> <tbody><tr> <th colspan="2">English short</th> <th>ISO </th></tr> <tr> <td>Sat 1 Jan 1977</td> <td><span class="nowrap">1977-01-01</span></td> <td bgcolor="lightgrey"><span class="nowrap">1976-W53-6</span> </td></tr> <tr> <td>Sun 2 Jan 1977</td> <td>1977-01-02</td> <td bgcolor="lightgrey">1976-W53-7 </td></tr> <tr> <td colspan="3"> </td></tr> <tr> <td>Sat 31 Dec 1977</td> <td>1977-12-31</td> <td>1977-W52-6 </td></tr> <tr> <td bgcolor="lightgrey">Sun 1 Jan 1978</td> <td bgcolor="lightgrey">1978-01-01</td> <td>1977-W52-7 </td></tr> <tr> <td bgcolor="lightgrey">Mon 2 Jan 1978</td> <td bgcolor="lightgrey">1978-01-02</td> <td bgcolor="lightgrey">1978-W01-1 </td></tr> <tr> <td colspan="3"> </td></tr> <tr> <td bgcolor="lightgrey">Sun 31 Dec 1978</td> <td bgcolor="lightgrey">1978-12-31</td> <td bgcolor="lightgrey">1978-W52-7 </td></tr> <tr> <td>Mon 1 Jan 1979</td> <td>1979-01-01</td> <td>1979-W01-1 </td></tr> <tr> <td colspan="3"> </td></tr> <tr> <td>Sun 30 Dec 1979</td> <td>1979-12-30</td> <td>1979-W52-7 </td></tr> <tr> <td>Mon 31 Dec 1979</td> <td>1979-12-31</td> <td bgcolor="lightgrey">1980-W01-1 </td></tr> <tr> <td bgcolor="lightgrey">Tue 1 Jan 1980</td> <td bgcolor="lightgrey">1980-01-01</td> <td bgcolor="lightgrey">1980-W01-2 </td></tr> <tr> <td colspan="3"> </td></tr> <tr> <td bgcolor="lightgrey">Sun 28 Dec 1980</td> <td bgcolor="lightgrey">1980-12-28</td> <td bgcolor="lightgrey">1980-W52-7 </td></tr> <tr> <td bgcolor="lightgrey">Mon 29 Dec 1980</td> <td bgcolor="lightgrey">1980-12-29</td> <td>1981-W01-1 </td></tr> <tr> <td bgcolor="lightgrey">Tue 30 Dec 1980</td> <td bgcolor="lightgrey">1980-12-30</td> <td>1981-W01-2 </td></tr> <tr> <td bgcolor="lightgrey">Wed 31 Dec 1980</td> <td bgcolor="lightgrey">1980-12-31</td> <td>1981-W01-3 </td></tr> <tr> <td>Thu 1 Jan 1981</td> <td>1981-01-01</td> <td>1981-W01-4 </td></tr> <tr> <td colspan="3"> </td></tr> <tr> <td>Thu 31 Dec 1981</td> <td>1981-12-31</td> <td>1981-W53-4 </td></tr> <tr> <td bgcolor="lightgrey">Fri 1 Jan 1982</td> <td bgcolor="lightgrey">1982-01-01</td> <td>1981-W53-5 </td></tr> <tr> <td bgcolor="lightgrey">Sat 2 Jan 1982</td> <td bgcolor="lightgrey">1982-01-02</td> <td>1981-W53-6 </td></tr> <tr> <td bgcolor="lightgrey">Sun 3 Jan 1982</td> <td bgcolor="lightgrey">1982-01-03</td> <td>1981-W53-7 </td></tr> <tr> <td colspan="3">Notes: <ul><li>Both years 1979 and 1979W start with the same day.</li> <li>1980 is a leap year. 1980W is 2 days shorter: <ul><li>1 day longer at the start,</li> <li>3 days shorter at the end.</li></ul></li> <li>1981W begins three days before the end of 1980.</li> <li>1981W has 53 weeks and ends three days into 1982.</li></ul> </td></tr></tbody></table> <p>A precise date is specified by the ISO week-numbering year in the format <var>YYYY</var>, a <b>week number</b> in the format <var>ww</var> prefixed by the letter 'W', and the <b>weekday number</b>, a digit <var>d</var> from 1 through 7, beginning with Monday and ending with Sunday. For example, the Gregorian date Wednesday, 27 November 2024 corresponds to day number 3 in the week number 48 of 2024, and is written as 2024-W48-3 (in extended form) or 2024W483 (in compact form). The ISO year is slightly offset to the Gregorian year; for example, Monday 30 December 2019 in the Gregorian calendar is the first day of week 1 of 2020 in the ISO calendar, and is written as 2020-W01-1 or 2020W011. </p> <meta property="mw:PageProp/toc" /> <div class="mw-heading mw-heading2"><h2 id="Relation_with_the_Gregorian_calendar">Relation with the Gregorian calendar</h2><span class="mw-editsection"><span class="mw-editsection-bracket">[</span><a href="/w/index.php?title=ISO_week_date&action=edit&section=1" title="Edit section: Relation with the Gregorian calendar"><span>edit</span></a><span class="mw-editsection-bracket">]</span></span></div> <p>The ISO week year number deviates from the Gregorian year number in one of three ways. The days differing are a Friday through Sunday, or a Saturday and Sunday, or just a Sunday, at the start of the Gregorian year (which are at the end of the previous ISO year) and a Monday through Wednesday, or a Monday and Tuesday, or just a Monday, at the end of the Gregorian year (which are in week 01 of the next ISO year). In the period 4 January to 28 December the ISO week year number is always equal to the Gregorian year number. The same is true for every Thursday. </p> <div class="mw-heading mw-heading3"><h3 id="First_week">First week</h3><span class="mw-editsection"><span class="mw-editsection-bracket">[</span><a href="/w/index.php?title=ISO_week_date&action=edit&section=2" title="Edit section: First week"><span>edit</span></a><span class="mw-editsection-bracket">]</span></span></div> <p>The <a href="/wiki/ISO_8601" title="ISO 8601">ISO 8601</a> definition for week 01 is the week with the first Thursday of the Gregorian year (i.e., of January) in it. The following definitions based on properties of this week are mutually equivalent, since the ISO week starts with Monday: </p> <ul><li>It is the first week with a majority (4 or more) of its days in January.</li> <li>Its first day is the Monday nearest to 1 January.</li> <li>It has 4 January in it. Hence the earliest possible first week extends from Monday 29 December (previous Gregorian year) to Sunday 4 January, the latest possible first week extends from Monday 4 January to Sunday 10 January.</li> <li>It has the year's first working day in it, if Saturdays, Sundays and 1 January are not working days.</li></ul> <p>If <b>1 January</b> is on a Monday, Tuesday, Wednesday or Thursday, it is in W01. If it is on a Friday, it is part of W53 of the previous year. If it is on a Saturday, it is part of the last week of the previous year which is numbered W52 in a common year and W53 in a leap year. If it is on a Sunday, it is part of W52 of the previous year. </p> <table class="wikitable"> <caption>Week date peculiarities at the beginning and end of a year </caption> <tbody><tr valign="bottom"> <th rowspan="2"><a href="/wiki/Dominical_letter" title="Dominical letter">Dominical <br />letter</a><sup id="cite_ref-fnp_1-0" class="reference"><a href="#cite_note-fnp-1"><span class="cite-bracket">[</span>a<span class="cite-bracket">]</span></a></sup> </th> <th colspan="7">Days at the start of January </th> <th colspan="4">Effect </th> <th colspan="7">Days at the end of December<sup id="cite_ref-fnp_1-1" class="reference"><a href="#cite_note-fnp-1"><span class="cite-bracket">[</span>a<span class="cite-bracket">]</span></a></sup> </th></tr> <tr valign="bottom"> <th>1<br />Mo</th> <th>2<br />Tu</th> <th>3<br />We</th> <th>4<br />Th</th> <th>5<br />Fr</th> <th>6<br />Sa</th> <th>7<br />Su </th> <th><span class="nowrap">W01-1<sup id="cite_ref-fn1_2-0" class="reference"><a href="#cite_note-fn1-2"><span class="cite-bracket">[</span>b<span class="cite-bracket">]</span></a></sup></span></th> <th>Week of<br />01 Jan</th> <th>...</th> <th>Week of<br />31 Dec<sup id="cite_ref-fnp_1-2" class="reference"><a href="#cite_note-fnp-1"><span class="cite-bracket">[</span>a<span class="cite-bracket">]</span></a></sup> </th> <th>1<sup id="cite_ref-fn2_3-0" class="reference"><a href="#cite_note-fn2-3"><span class="cite-bracket">[</span>c<span class="cite-bracket">]</span></a></sup><br />Mo</th> <th>2<br />Tu</th> <th>3<br />We</th> <th>4<br />Th</th> <th>5<br />Fr</th> <th>6<br />Sa</th> <th>7<br />Su </th></tr> <tr align="center"> <th><a href="/wiki/Common_year_starting_on_Monday" title="Common year starting on Monday">G</a> (<a href="/wiki/Leap_year_starting_on_Monday" title="Leap year starting on Monday">F</a>) </th> <td>01</td> <td>02</td> <td>03</td> <td>04</td> <td>05</td> <td>06</td> <td>07 </td> <td style="background:#9EFF9E;color:black;vertical-align:middle;text-align:center;" class="table-yes">01 Jan</td> <td rowspan="4" style="background:#9EFF9E;color:black;vertical-align:middle;text-align:center;" class="table-yes">W01</td> <td rowspan="7">...</td> <td rowspan="2" style="background:#FFC7C7;color:black;vertical-align:middle;text-align:center;" class="table-no">W01 </td> <td><span class="nowrap">31 (30)</span></td> <td><span style="visibility:hidden;color:transparent;"> </span> (31)</td> <td></td> <td></td> <td></td> <td></td> <td> </td></tr> <tr align="center"> <th><a href="/wiki/Common_year_starting_on_Tuesday" title="Common year starting on Tuesday">F</a> (<a href="/wiki/Leap_year_starting_on_Tuesday" title="Leap year starting on Tuesday">E</a>) </th> <td></td> <td>01</td> <td>02</td> <td>03</td> <td>04</td> <td>05</td> <td>06 </td> <td style="background:#FFC7C7;color:black;vertical-align:middle;text-align:center;" class="table-no">31 Dec </td> <td>30 (29)</td> <td><span class="nowrap">31 (30)</span></td> <td><span style="visibility:hidden;color:transparent;"> </span> (31)</td> <td></td> <td></td> <td></td> <td> </td></tr> <tr align="center"> <th><a href="/wiki/Common_year_starting_on_Wednesday" title="Common year starting on Wednesday">E</a> (<a href="/wiki/Leap_year_starting_on_Wednesday" title="Leap year starting on Wednesday">D</a>) </th> <td></td> <td></td> <td>01</td> <td>02</td> <td>03</td> <td>04</td> <td>05 </td> <td style="background:#FFC7C7;color:black;vertical-align:middle;text-align:center;" class="table-no">30 Dec</td> <td title="W53 when ending year is leap, W01 otherwise." style="background:#FFB; color:black;vertical-align:middle;text-align:center;" class="table-partial">W01 (W53) </td> <td>29 (28)</td> <td>30 (29)</td> <td><span class="nowrap">31 (30)</span></td> <td><span style="visibility:hidden;color:transparent;"> </span> (31)</td> <td></td> <td></td> <td> </td></tr> <tr align="center"> <th><a href="/wiki/Common_year_starting_on_Thursday" title="Common year starting on Thursday">D</a>(<a href="/wiki/Leap_year_starting_on_Thursday" title="Leap year starting on Thursday">C</a>) </th> <td></td> <td></td> <td></td> <td>01</td> <td>02</td> <td>03</td> <td>04 </td> <td style="background:#FFC7C7;color:black;vertical-align:middle;text-align:center;" class="table-no">29 Dec</td> <td style="background:#9EFF9E;color:black;vertical-align:middle;text-align:center;" class="table-yes">W53 </td> <td>28 (27)</td> <td>29 (28)</td> <td>30 (29)</td> <td><span class="nowrap">31 (30)</span></td> <td><span style="visibility:hidden;color:transparent;"> </span> (31)</td> <td></td> <td> </td></tr> <tr align="center"> <th><a href="/wiki/Common_year_starting_on_Friday" title="Common year starting on Friday">C</a> (<a href="/wiki/Leap_year_starting_on_Friday" title="Leap year starting on Friday">B</a>) </th> <td></td> <td></td> <td></td> <td></td> <td>01</td> <td>02</td> <td>03 </td> <td style="background:#9EFF9E;color:black;vertical-align:middle;text-align:center;" class="table-yes">04 Jan</td> <td style="background:#FFC7C7;color:black;vertical-align:middle;text-align:center;" class="table-no">W53</td> <td rowspan="2" style="background:#9EFF9E;color:black;vertical-align:middle;text-align:center;" class="table-yes">W52 </td> <td>27 (26)</td> <td>28 (27)</td> <td>29 (28)</td> <td>30 (29)</td> <td><span class="nowrap">31 (30)</span></td> <td><span style="visibility:hidden;color:transparent;"> </span> (31)</td> <td> </td></tr> <tr align="center"> <th><a href="/wiki/Common_year_starting_on_Saturday" title="Common year starting on Saturday">B</a> (<a href="/wiki/Leap_year_starting_on_Saturday" title="Leap year starting on Saturday">A</a>) </th> <td></td> <td></td> <td></td> <td></td> <td></td> <td>01</td> <td>02 </td> <td style="background:#9EFF9E;color:black;vertical-align:middle;text-align:center;" class="table-yes">03 Jan</td> <td title="W53 when ending year is leap, W52 otherwise." style="background:#FFC7C7;color:black;vertical-align:middle;text-align:center;" class="table-no">W52 (W53)<sup id="cite_ref-fns_4-0" class="reference"><a href="#cite_note-fns-4"><span class="cite-bracket">[</span>d<span class="cite-bracket">]</span></a></sup> </td> <td>26 (25)</td> <td>27 (26)</td> <td>28 (27)</td> <td>29 (28)</td> <td>30 (29)</td> <td><span class="nowrap">31 (30)</span></td> <td><span style="visibility:hidden;color:transparent;"> </span> (31) </td></tr> <tr align="center"> <th><a href="/wiki/Common_year_starting_on_Sunday" title="Common year starting on Sunday">A</a> (<a href="/wiki/Leap_year_starting_on_Sunday" title="Leap year starting on Sunday">G</a>) </th> <td></td> <td></td> <td></td> <td></td> <td></td> <td></td> <td>01 </td> <td style="background:#9EFF9E;color:black;vertical-align:middle;text-align:center;" class="table-yes">02 Jan</td> <td style="background:#FFC7C7;color:black;vertical-align:middle;text-align:center;" class="table-no">W52</td> <td title="31 December is in W01 only if it is in a leap year." style="background:#FFB; color:black;vertical-align:middle;text-align:center;" class="table-partial">W52 (W01) </td> <td>25 (31)</td> <td>26 (25)</td> <td>27 (26)</td> <td>28 (27)</td> <td>29 (28)</td> <td>30 (29)</td> <td><span class="nowrap">31 (30)</span> </td></tr></tbody></table> <p><b>Notes</b> </p> <style data-mw-deduplicate="TemplateStyles:r1239543626">.mw-parser-output .reflist{margin-bottom:0.5em;list-style-type:decimal}@media screen{.mw-parser-output .reflist{font-size:90%}}.mw-parser-output .reflist .references{font-size:100%;margin-bottom:0;list-style-type:inherit}.mw-parser-output .reflist-columns-2{column-width:30em}.mw-parser-output .reflist-columns-3{column-width:25em}.mw-parser-output .reflist-columns{margin-top:0.3em}.mw-parser-output .reflist-columns ol{margin-top:0}.mw-parser-output .reflist-columns li{page-break-inside:avoid;break-inside:avoid-column}.mw-parser-output .reflist-upper-alpha{list-style-type:upper-alpha}.mw-parser-output .reflist-upper-roman{list-style-type:upper-roman}.mw-parser-output .reflist-lower-alpha{list-style-type:lower-alpha}.mw-parser-output .reflist-lower-greek{list-style-type:lower-greek}.mw-parser-output .reflist-lower-roman{list-style-type:lower-roman}</style><div class="reflist reflist-lower-alpha"> <div class="mw-references-wrap"><ol class="references"> <li id="cite_note-fnp-1"><span class="mw-cite-backlink">^ <a href="#cite_ref-fnp_1-0"><sup><i><b>a</b></i></sup></a> <a href="#cite_ref-fnp_1-1"><sup><i><b>b</b></i></sup></a> <a href="#cite_ref-fnp_1-2"><sup><i><b>c</b></i></sup></a></span> <span class="reference-text">Partial dates in parentheses, ( ), apply to leap years.</span> </li> <li id="cite_note-fn1-2"><span class="mw-cite-backlink"><b><a href="#cite_ref-fn1_2-0">^</a></b></span> <span class="reference-text">First date of the <b>first</b> week in the year.</span> </li> <li id="cite_note-fn2-3"><span class="mw-cite-backlink"><b><a href="#cite_ref-fn2_3-0">^</a></b></span> <span class="reference-text">First date of the <b>last</b> week in the year.</span> </li> <li id="cite_note-fns-4"><span class="mw-cite-backlink"><b><a href="#cite_ref-fns_4-0">^</a></b></span> <span class="reference-text">W53 for the week of 1 January in common years starting on Saturday (B) applies only if the previous year was a leap year starting on Thursday (DC).</span> </li> </ol></div></div> <div class="mw-heading mw-heading3"><h3 id="Last_week">Last week</h3><span class="mw-editsection"><span class="mw-editsection-bracket">[</span><a href="/w/index.php?title=ISO_week_date&action=edit&section=3" title="Edit section: Last week"><span>edit</span></a><span class="mw-editsection-bracket">]</span></span></div> <p>The last week of the ISO week-numbering year, i.e. W52 or W53, is the week before W01 of the next year. This week's properties are: </p> <ul><li>It has the year's last Thursday in it.</li> <li>It is the last week with a majority (4 or more) of its days in December.</li> <li>Its middle day, Thursday, falls in the ending year.</li> <li>Its last day is the Sunday nearest to 31 December.</li> <li>It has 28 December in it.</li></ul> <p>Hence the earliest possible last week extends from Monday 22 December to Sunday 28 December, the latest possible last week extends from Monday 28 December to Sunday 3 January. </p><p>If 31 December is on a Monday, Tuesday, or Wednesday it is in W01 of the next year. If it is on a Thursday, it is in W53 of the year just ending. If on a Friday it is in W52 of the year just ending in common years and W53 in leap years. If on a Saturday or Sunday, it is in W52 of the year just ending. </p> <table class="wikitable"> <caption>Summary of last weeks </caption> <tbody><tr> <th>01 Jan</th> <th>W01-1</th> <th colspan="3">Common year (365 − 1 or + 6)</th> <th colspan="3">Leap year (366 − 2 or + 5) </th></tr> <tr> <td>Mon</td> <td>01 Jan</td> <td>G</td> <td>+0</td> <td>−1</td> <td>GF</td> <td>+0</td> <td>−2 </td></tr> <tr> <td>Tue</td> <td>31 Dec</td> <td>F</td> <td>+1</td> <td>−2</td> <td>FE</td> <td>+1</td> <td>−3 </td></tr> <tr> <td>Wed</td> <td>30 Dec</td> <td>E</td> <td>+2</td> <td>−3</td> <td>ED</td> <td>+<b>2</b></td> <td>+<b>3</b> </td></tr> <tr> <td>Thu</td> <td>29 Dec</td> <td>D</td> <td>+<b>3</b></td> <td>+<b>3</b></td> <td>DC</td> <td>+<b>3</b></td> <td>+<b>2</b> </td></tr> <tr> <td>Fri</td> <td>04 Jan</td> <td>C</td> <td>−3</td> <td>+2</td> <td>CB</td> <td>−3</td> <td>+1 </td></tr> <tr> <td>Sat</td> <td>03 Jan</td> <td>B</td> <td>−2</td> <td>+1</td> <td>BA</td> <td>−2</td> <td>+0 </td></tr> <tr> <td>Sun</td> <td>02 Jan</td> <td>A</td> <td>−1</td> <td>+0</td> <td>AG</td> <td>−1</td> <td>−1 </td></tr></tbody></table> <div class="mw-heading mw-heading3"><h3 id="Weeks_per_year">Weeks per year</h3><span class="mw-editsection"><span class="mw-editsection-bracket">[</span><a href="/w/index.php?title=ISO_week_date&action=edit&section=4" title="Edit section: Weeks per year"><span>edit</span></a><span class="mw-editsection-bracket">]</span></span></div> <p>The <i>long years</i>, with 53 weeks in them, can be described by any of the following equivalent definitions: </p> <ul><li>any year <i>starting</i> on Thursday (<a href="/wiki/Dominical_letter" title="Dominical letter">dominical letter</a> <a href="/wiki/Common_year_starting_on_Thursday" title="Common year starting on Thursday">D</a> or <a href="/wiki/Leap_year_starting_on_Thursday" title="Leap year starting on Thursday">DC</a>) and any leap year <i>starting</i> on Wednesday (<a href="/wiki/Leap_year_starting_on_Wednesday" title="Leap year starting on Wednesday">ED</a>)</li> <li>any year <i>ending</i> on Thursday (D, ED) and any leap year <i>ending</i> on Friday (DC)</li> <li>years in which 1 January or 31 December are Thursdays</li></ul> <p>All other week-numbering years are <i>short years</i> and have 52 weeks. </p><p>The number of weeks in a given year is equal to the corresponding week number of 28 December, because it is the only date that is always in the last week of the year since it is a week before 4 January which is always in the first week of the following year. </p><p>Using only the ordinal year number <i>y</i>, the number of weeks in that year can be determined from a function, <span class="mwe-math-element"><span class="mwe-math-mathml-inline mwe-math-mathml-a11y" style="display: none;"><math xmlns="http://www.w3.org/1998/Math/MathML" alttext="{\displaystyle p(y)}"> <semantics> <mrow class="MJX-TeXAtom-ORD"> <mstyle displaystyle="true" scriptlevel="0"> <mi>p</mi> <mo stretchy="false">(</mo> <mi>y</mi> <mo stretchy="false">)</mo> </mstyle> </mrow> <annotation encoding="application/x-tex">{\displaystyle p(y)}</annotation> </semantics> </math></span><img src="https://wikimedia.org/api/rest_v1/media/math/render/svg/6b2c472d927e5b59281522a993493664cd3f4422" class="mwe-math-fallback-image-inline mw-invert skin-invert" aria-hidden="true" style="vertical-align: -0.838ex; margin-left: -0.089ex; width:4.224ex; height:2.843ex;" alt="{\displaystyle p(y)}"></span>, that returns the day of the week of 31 December:<sup id="cite_ref-Gent3_5-0" class="reference"><a href="#cite_note-Gent3-5"><span class="cite-bracket">[</span>1<span class="cite-bracket">]</span></a></sup> </p> <dl><dd><span class="mwe-math-element"><span class="mwe-math-mathml-inline mwe-math-mathml-a11y" style="display: none;"><math xmlns="http://www.w3.org/1998/Math/MathML" alttext="{\displaystyle {\begin{aligned}p(y)&=\left(y+\left\lfloor {\frac {y}{4}}\right\rfloor -\left\lfloor {\frac {y}{100}}\right\rfloor +\left\lfloor {\frac {y}{400}}\right\rfloor \right){\bmod {7}}\\{\text{weeks}}(y)&=52+{\begin{cases}1{\text{ (long)}}&{\text{if }}p(y)=4{\text{, i.e. current year ends Thursday}}\\&{\text{or }}p(y-1)=3{\text{, i.e. previous year ends Wednesday}}\\0{\text{ (short)}}&{\text{otherwise}}\end{cases}}\end{aligned}}}"> <semantics> <mrow class="MJX-TeXAtom-ORD"> <mstyle displaystyle="true" scriptlevel="0"> <mrow class="MJX-TeXAtom-ORD"> <mtable columnalign="right left right left right left right left right left right left" rowspacing="3pt" columnspacing="0em 2em 0em 2em 0em 2em 0em 2em 0em 2em 0em" displaystyle="true"> <mtr> <mtd> <mi>p</mi> <mo stretchy="false">(</mo> <mi>y</mi> <mo stretchy="false">)</mo> </mtd> <mtd> <mi></mi> <mo>=</mo> <mrow> <mo>(</mo> <mrow> <mi>y</mi> <mo>+</mo> <mrow> <mo>⌊</mo> <mrow class="MJX-TeXAtom-ORD"> <mfrac> <mi>y</mi> <mn>4</mn> </mfrac> </mrow> <mo>⌋</mo> </mrow> <mo>−</mo> <mrow> <mo>⌊</mo> <mrow class="MJX-TeXAtom-ORD"> <mfrac> <mi>y</mi> <mn>100</mn> </mfrac> </mrow> <mo>⌋</mo> </mrow> <mo>+</mo> <mrow> <mo>⌊</mo> <mrow class="MJX-TeXAtom-ORD"> <mfrac> <mi>y</mi> <mn>400</mn> </mfrac> </mrow> <mo>⌋</mo> </mrow> </mrow> <mo>)</mo> </mrow> <mrow class="MJX-TeXAtom-ORD"> <mo lspace="thickmathspace" rspace="thickmathspace">mod</mo> <mrow class="MJX-TeXAtom-ORD"> <mn>7</mn> </mrow> </mrow> </mtd> </mtr> <mtr> <mtd> <mrow class="MJX-TeXAtom-ORD"> <mtext>weeks</mtext> </mrow> <mo stretchy="false">(</mo> <mi>y</mi> <mo stretchy="false">)</mo> </mtd> <mtd> <mi></mi> <mo>=</mo> <mn>52</mn> <mo>+</mo> <mrow class="MJX-TeXAtom-ORD"> <mrow> <mo>{</mo> <mtable columnalign="left left" rowspacing=".2em" columnspacing="1em" displaystyle="false"> <mtr> <mtd> <mn>1</mn> <mrow class="MJX-TeXAtom-ORD"> <mtext> (long)</mtext> </mrow> </mtd> <mtd> <mrow class="MJX-TeXAtom-ORD"> <mtext>if </mtext> </mrow> <mi>p</mi> <mo stretchy="false">(</mo> <mi>y</mi> <mo stretchy="false">)</mo> <mo>=</mo> <mn>4</mn> <mrow class="MJX-TeXAtom-ORD"> <mtext>, i.e. current year ends Thursday</mtext> </mrow> </mtd> </mtr> <mtr> <mtd /> <mtd> <mrow class="MJX-TeXAtom-ORD"> <mtext>or </mtext> </mrow> <mi>p</mi> <mo stretchy="false">(</mo> <mi>y</mi> <mo>−</mo> <mn>1</mn> <mo stretchy="false">)</mo> <mo>=</mo> <mn>3</mn> <mrow class="MJX-TeXAtom-ORD"> <mtext>, i.e. previous year ends Wednesday</mtext> </mrow> </mtd> </mtr> <mtr> <mtd> <mn>0</mn> <mrow class="MJX-TeXAtom-ORD"> <mtext> (short)</mtext> </mrow> </mtd> <mtd> <mrow class="MJX-TeXAtom-ORD"> <mtext>otherwise</mtext> </mrow> </mtd> </mtr> </mtable> <mo fence="true" stretchy="true" symmetric="true"></mo> </mrow> </mrow> </mtd> </mtr> </mtable> </mrow> </mstyle> </mrow> <annotation encoding="application/x-tex">{\displaystyle {\begin{aligned}p(y)&=\left(y+\left\lfloor {\frac {y}{4}}\right\rfloor -\left\lfloor {\frac {y}{100}}\right\rfloor +\left\lfloor {\frac {y}{400}}\right\rfloor \right){\bmod {7}}\\{\text{weeks}}(y)&=52+{\begin{cases}1{\text{ (long)}}&{\text{if }}p(y)=4{\text{, i.e. current year ends Thursday}}\\&{\text{or }}p(y-1)=3{\text{, i.e. previous year ends Wednesday}}\\0{\text{ (short)}}&{\text{otherwise}}\end{cases}}\end{aligned}}}</annotation> </semantics> </math></span><img src="https://wikimedia.org/api/rest_v1/media/math/render/svg/d1b950f0d43b769020a98fdb8922f211fb805048" class="mwe-math-fallback-image-inline mw-invert skin-invert" aria-hidden="true" style="vertical-align: -6.338ex; width:82.309ex; height:13.843ex;" alt="{\displaystyle {\begin{aligned}p(y)&=\left(y+\left\lfloor {\frac {y}{4}}\right\rfloor -\left\lfloor {\frac {y}{100}}\right\rfloor +\left\lfloor {\frac {y}{400}}\right\rfloor \right){\bmod {7}}\\{\text{weeks}}(y)&=52+{\begin{cases}1{\text{ (long)}}&{\text{if }}p(y)=4{\text{, i.e. current year ends Thursday}}\\&{\text{or }}p(y-1)=3{\text{, i.e. previous year ends Wednesday}}\\0{\text{ (short)}}&{\text{otherwise}}\end{cases}}\end{aligned}}}"></span></dd></dl> <table class="wikitable floatright"> <caption>Long years per 400-year leap-cycle, highlighted ones also have 29 Feb in them; adding 2000 gives current year numbers </caption> <tbody><tr> <th>Subcycle </th> <th>+6</th> <th>+5</th> <th>+6</th> <th>+5</th> <th>+6 </th></tr> <tr> <th>28<sub>1</sub> </th> <td><b>004</b></td> <td>009</td> <td>015</td> <td><b>020</b></td> <td>026 </td></tr> <tr> <th>28<sub>2</sub> </th> <td><b>032</b></td> <td>037</td> <td>043</td> <td><b>048</b></td> <td>054 </td></tr> <tr> <th>28<sub>3</sub> </th> <td><b>060</b></td> <td>065</td> <td>071</td> <td><b>076</b></td> <td>082 </td></tr> <tr> <th rowspan="2">40<sub>1</sub> </th> <td><b>088</b></td> <td>093</td> <td>099</td> <td></td> <td> </td></tr> <tr> <td></td> <td>105</td> <td>111</td> <td><b>116</b></td> <td>122 </td></tr> <tr> <th>28<sub>4</sub> </th> <td><b>128</b></td> <td>133</td> <td>139</td> <td><b>144</b></td> <td>150 </td></tr> <tr> <th>28<sub>5</sub> </th> <td><b>156</b></td> <td>161</td> <td>167</td> <td><b>172</b></td> <td>178 </td></tr> <tr> <th rowspan="2">40<sub>2</sub> </th> <td><b>184</b></td> <td>189</td> <td>195</td> <td></td> <td> </td></tr> <tr> <td></td> <td>201</td> <td>207</td> <td><b>212</b></td> <td>218 </td></tr> <tr> <th>28<sub>6</sub> </th> <td><b>224</b></td> <td>229</td> <td>235</td> <td><b>240</b></td> <td>246 </td></tr> <tr> <th>28<sub>7</sub> </th> <td><b>252</b></td> <td>257</td> <td>263</td> <td><b>268</b></td> <td>274 </td></tr> <tr> <th rowspan="2">40<sub>3</sub> </th> <td><b>280</b></td> <td>285</td> <td>291</td> <td><b>296</b></td> <td> </td></tr> <tr> <td></td> <td></td> <td>303</td> <td><b>308</b></td> <td>314 </td></tr> <tr> <th>28<sub>8</sub> </th> <td><b>320</b></td> <td>325</td> <td>331</td> <td><b>336</b></td> <td>342 </td></tr> <tr> <th>28<sub>9</sub> </th> <td><b>348</b></td> <td>353</td> <td>359</td> <td><b>364</b></td> <td>370 </td></tr> <tr> <th>28<sub>10</sub> </th> <td><b>376</b></td> <td>381</td> <td>387</td> <td><b>392</b></td> <td>398 </td></tr></tbody></table> <p>On average, a year has 53 weeks every <link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1154941027"><span class="frac"><span class="num">400</span>⁄<span class="den">71</span></span> = 5.6338... years; there are 43 times when these long years are 6 years apart, 27 times when they are 5 years apart, and once they are 7 years apart (between years 296 and 303). The Gregorian years corresponding to these 71 long years can be subdivided as follows: </p> <ul><li>27 Gregorian leap years, emphasized in the list above: <ul><li>14 <a href="/wiki/Leap_year_starting_on_Thursday" title="Leap year starting on Thursday">starting on Thursday, hence ending on Friday</a>, and</li> <li>13 <a href="/wiki/Leap_year_starting_on_Wednesday" title="Leap year starting on Wednesday">starting on Wednesday, hence ending on Thursday</a>;</li></ul></li> <li>44 Gregorian common years <a href="/wiki/Common_year_starting_on_Thursday" title="Common year starting on Thursday">starting, hence also ending on Thursday</a>.</li></ul> <p>The Gregorian years corresponding to the other 329 short years (neither starting nor ending with Thursday) can also be subdivided as follows: </p> <ul><li>70 are Gregorian leap years.</li> <li>259 are Gregorian common years.</li></ul> <p>Thus, within a 400-year cycle: </p> <ul><li>27 week years are <i>5 days longer</i> than the month years (371 − 366), 6.75%.</li> <li>44 week years are <i>6 days longer</i> than the month years (371 − 365), 11%.</li> <li>70 week years are <i>2 days shorter</i> than the month years (364 − 366), 17.5%.</li> <li>259 week years are <i>1 day shorter</i> than the month years (364 − 365), 64.75%.</li></ul> <p>The table shows the long years in a 400-year cycle. There are 28 years, i.e. a <a href="/wiki/Solar_cycle_(calendar)" title="Solar cycle (calendar)">Julian solar cycle</a>, between long years in the same column except when the century changes, when there are 40 years between the long years in the next century and the last completely filled row (or subcycle) of the previous century. There are ten regular subcycles of 28 years each and three subcycles of 40 years each. The 40-year subcycles 085–124 and 181–220 are equal, but the middle long year within the subcycle 277–316 would have to occur in 297 instead of 296 to be also the same. This illustrates the only, abnormal 7-year gap between long years. </p> <div class="mw-heading mw-heading3"><h3 id="Weeks_per_month">Weeks per month</h3><span class="mw-editsection"><span class="mw-editsection-bracket">[</span><a href="/w/index.php?title=ISO_week_date&action=edit&section=5" title="Edit section: Weeks per month"><span>edit</span></a><span class="mw-editsection-bracket">]</span></span></div> <p>The ISO standard does not define any association of weeks to months. A date is either expressed with a month and day-of-the-month, or with a week and day-of-the-week, never a mix. </p><p>Weeks are a prominent entity in accounting where annual statistics benefit from regularity throughout the <a href="/wiki/Fiscal_year" title="Fiscal year">years</a>. Therefore, a fixed length of 13 weeks per <a href="/wiki/Fiscal_quarter" class="mw-redirect" title="Fiscal quarter">quarter</a> is usually chosen in practice. These quarters may then be subdivided into <a href="/wiki/Hanke%E2%80%93Henry_Permanent_Calendar" title="Hanke–Henry Permanent Calendar">5 + 4 + 4 weeks</a>, <a href="/wiki/Sym454" class="mw-redirect" title="Sym454">4 + 5 + 4 weeks</a> or <a href="/wiki/4%E2%80%934%E2%80%935_calendar" title="4–4–5 calendar">4 + 4 + 5 weeks</a>. The final quarter has 14 weeks in it when there are 53 weeks in the year. </p><p>When it is necessary to allocate a week to a single month, the rule for first week of the year might be applied, although ISO 8601-1 does not consider this case explicitly. The resulting pattern would be irregular. There would be 4 months of 5 weeks per normal, 52-week year, or 5 such months in a long, 53-week year. Although the days of a month (except February) always belong to 5 and sometimes 6 different weeks, there would never be 6 weeks belonging to a single month. The 5-week months would meet one of the following three criteria: </p> <ul><li>The first day of the month is a ... <ul><li>Thursday and the month has 29 through 31 days.</li> <li>Wednesday and the month has 30 or 31 days.</li> <li>Tuesday and the month has 31 days, ending on a Thursday.</li></ul></li> <li>Equivalently, the last day of the month is a ... <ul><li>Thursday and it is not the 28th.</li> <li>Friday and it is not in February.</li> <li>Saturday and it is the 31st.</li></ul></li></ul> <div class="mw-heading mw-heading3"><h3 id="Dates_with_fixed_week_number">Dates with fixed week number</h3><span class="mw-editsection"><span class="mw-editsection-bracket">[</span><a href="/w/index.php?title=ISO_week_date&action=edit&section=6" title="Edit section: Dates with fixed week number"><span>edit</span></a><span class="mw-editsection-bracket">]</span></span></div> <table class="wikitable floatright"> <caption>Overview of dates with a fixed week number </caption> <tbody><tr> <th>Month</th> <th colspan="5">Days</th> <th>Weeks </th></tr> <tr> <th>January </th> <td><a href="/wiki/January_4" title="January 4">04</a></td> <td><a href="/wiki/January_11" title="January 11">11</a></td> <td><a href="/wiki/January_18" title="January 18">18</a></td> <td><a href="/wiki/January_25" title="January 25">25</a></td> <td> </td> <td>W01 – W04 </td></tr> <tr> <th>February </th> <td><a href="/wiki/February_1" title="February 1">01</a></td> <td><a href="/wiki/February_8" title="February 8">08</a></td> <td><a href="/wiki/February_15" title="February 15">15</a></td> <td><a href="/wiki/February_22" title="February 22">22</a></td> <td style="background: #DFD; color:black; vertical-align: middle; text-align: center;"><a href="/wiki/February_29" title="February 29">29</a> </td> <td>W05 – W09 </td></tr> <tr> <td colspan="7" style="max-width: 20ex">Later dates differ in any <a href="/wiki/Leap_year_starting_on_Thursday" title="Leap year starting on Thursday">leap year starting on Thursday</a>: </td></tr> <tr> <th>March </th> <td><a href="/wiki/March_1" title="March 1">01</a></td> <td><a href="/wiki/March_8" title="March 8">08</a></td> <td><a href="/wiki/March_15" title="March 15">15</a></td> <td><a href="/wiki/March_22" title="March 22">22</a></td> <td><a href="/wiki/March_29" title="March 29">29</a> </td> <td>W09 – W13 </td></tr> <tr> <th>April </th> <td><a href="/wiki/April_5" title="April 5">05</a></td> <td><a href="/wiki/April_12" title="April 12">12</a></td> <td><a href="/wiki/April_19" title="April 19">19</a></td> <td><a href="/wiki/April_26" title="April 26">26</a></td> <td> </td> <td>W14 – W17 </td></tr> <tr> <th>May </th> <td><a href="/wiki/May_3" title="May 3">03</a></td> <td><a href="/wiki/May_10" title="May 10">10</a></td> <td><a href="/wiki/May_17" title="May 17">17</a></td> <td><a href="/wiki/May_24" title="May 24">24</a></td> <td><a href="/wiki/May_31" title="May 31">31</a> </td> <td>W18 – W22 </td></tr> <tr> <th>June </th> <td><a href="/wiki/June_7" title="June 7">07</a></td> <td><a href="/wiki/June_14" title="June 14">14</a></td> <td><a href="/wiki/June_21" title="June 21">21</a></td> <td><a href="/wiki/June_28" title="June 28">28</a></td> <td> </td> <td>W23 – W26 </td></tr> <tr> <th>July </th> <td><a href="/wiki/July_5" title="July 5">05</a></td> <td><a href="/wiki/July_12" title="July 12">12</a></td> <td><a href="/wiki/July_19" title="July 19">19</a></td> <td><a href="/wiki/July_26" title="July 26">26</a></td> <td> </td> <td>W27 – W30 </td></tr> <tr> <th>August </th> <td><a href="/wiki/August_2" title="August 2">02</a></td> <td><a href="/wiki/August_9" title="August 9">09</a></td> <td><a href="/wiki/August_16" title="August 16">16</a></td> <td><a href="/wiki/August_23" title="August 23">23</a></td> <td><a href="/wiki/August_30" title="August 30">30</a> </td> <td>W31 – W35 </td></tr> <tr> <th>September </th> <td><a href="/wiki/September_6" title="September 6">06</a></td> <td><a href="/wiki/September_13" title="September 13">13</a></td> <td><a href="/wiki/September_20" title="September 20">20</a></td> <td><a href="/wiki/September_27" title="September 27">27</a></td> <td> </td> <td>W36 – W39 </td></tr> <tr> <th>October </th> <td><a href="/wiki/October_4" title="October 4">04</a></td> <td><a href="/wiki/October_11" title="October 11">11</a></td> <td><a href="/wiki/October_18" title="October 18">18</a></td> <td><a href="/wiki/October_25" title="October 25">25</a></td> <td> </td> <td>W40 – W43 </td></tr> <tr> <th>November </th> <td><a href="/wiki/November_1" title="November 1">01</a></td> <td><a href="/wiki/November_8" title="November 8">08</a></td> <td><a href="/wiki/November_15" title="November 15">15</a></td> <td><a href="/wiki/November_22" title="November 22">22</a></td> <td><a href="/wiki/November_29" title="November 29">29</a> </td> <td>W44 – W48 </td></tr> <tr> <th>December </th> <td><a href="/wiki/December_6" title="December 6">06</a></td> <td><a href="/wiki/December_13" title="December 13">13</a></td> <td><a href="/wiki/December_20" title="December 20">20</a></td> <td><a href="/wiki/December_27" title="December 27">27</a></td> <td> </td> <td>W49 – W52 </td></tr></tbody></table> <p>For all years, 8 days have a fixed ISO week number (between W01 and W08) in January and February. With the exception of leap years starting on Thursday, dates with fixed week numbers occur in all months of the year (for 1 day of each ISO week W01 to W52). </p><p>During leap years starting on Thursday (i.e. the 13 years numbered 004, 032, 060, 088, 128, 156, 184, 224, 252, 280, 320, 348, 376 in a 400-year cycle), the ISO week numbers are incremented by 1 from March to the rest of the year. This last occurred in 1976 and 2004, and will next occur in 2032. These exceptions are happening between years that are most often 28 years apart, or 40 years apart for 3 pairs of successive years: from year 088 to 128, from year 184 to 224, and from year 280 to 320. They will never be 12 years apart. The only leap years that can occur 12 years apart are leap years starting on Sunday, Tuesday, Wednesday and Friday. </p><p>The day of the week for these days are related to <a href="/wiki/Doomsday_rule" title="Doomsday rule">the "Doomsday" algorithm</a>, which calculates the weekday that the last day of February falls on. The dates listed in the table are all one day after the Doomsday, except that in January and February of leap years the dates themselves are Doomsdays. In leap years, the week number is <a href="/wiki/Doomsday_(weekday)#Overview_of_all_Doomsdays" class="mw-redirect" title="Doomsday (weekday)">the rank number of its Doomsday</a>. </p> <div class="mw-heading mw-heading3"><h3 id="Equal_weeks">Equal weeks</h3><span class="mw-editsection"><span class="mw-editsection-bracket">[</span><a href="/w/index.php?title=ISO_week_date&action=edit&section=7" title="Edit section: Equal weeks"><span>edit</span></a><span class="mw-editsection-bracket">]</span></span></div> <p>Some pairs and triplets of ISO weeks have the same days of the month: </p> <ul><li>W02 and W41 in common years</li> <li>W03 with W42 in common years and with W15 and W28 in leap years</li> <li>W04 and W43 in common years and with W16 and W29 in leap years</li> <li>W05 and W44 in common years</li> <li>W06 with W10 and W45 in common years and with W32 in leap years</li> <li>W07 with W11 and W46 in common years and with W33 in leap years</li> <li>W08 with W12 and W47 in common years and with W34 in leap years</li> <li>W10 and W45</li> <li>W11 and W46</li> <li>W12 and W47</li> <li>W15 and W28</li> <li>W16 and W29</li> <li>W37 and W50</li> <li>W38 and W51</li></ul> <p>Some other weeks, i.e. W09, W19 through W26, W31 and W35 never share their days of the month ordinals with any other week of the same year. </p> <div class="mw-heading mw-heading2"><h2 id="Advantages">Advantages</h2><span class="mw-editsection"><span class="mw-editsection-bracket">[</span><a href="/w/index.php?title=ISO_week_date&action=edit&section=8" title="Edit section: Advantages"><span>edit</span></a><span class="mw-editsection-bracket">]</span></span></div> <ul><li>All weeks have exactly 7 days, i.e. there are no fractional weeks.</li> <li>Every week belongs to a single year, i.e. there are no ambiguous or double-assigned weeks.</li> <li>The date directly tells the weekday.</li> <li>All week-numbering years start with a Monday and end with a Sunday.</li> <li>When used by itself without using the concept of month, all week-numbering years are the same except that some years have a week 53 at the end.</li> <li>The weeks are the same as used with the Gregorian calendar.</li></ul> <div class="mw-heading mw-heading2"><h2 id="Differences_to_other_calendars">Differences to other calendars</h2><span class="mw-editsection"><span class="mw-editsection-bracket">[</span><a href="/w/index.php?title=ISO_week_date&action=edit&section=9" title="Edit section: Differences to other calendars"><span>edit</span></a><span class="mw-editsection-bracket">]</span></span></div> <p>Solar astronomic phenomena, such as <a href="/wiki/Equinox" title="Equinox">equinoxes</a> and <a href="/wiki/Solstice" title="Solstice">solstices</a>, vary in the Gregorian calendar over a range spanning three days, over the course of each 400-year cycle, while the ISO Week Date calendar has a range spanning 9 days. For example, there are March equinoxes on 1920-W12-6 and 2077-W11-5 in UT. </p><p>The year number of the ISO week very often differs from the Gregorian year number for dates close to 1 January. For example, 29 December 1986 is ISO 1987-W01-1, i.e., it is in year 1987 instead of 1986. A programming bug confusing these two year numbers is probably the cause of some <a href="/wiki/Android_(operating_system)" title="Android (operating system)">Android</a> users of <a href="/wiki/Twitter" title="Twitter">Twitter</a> being unable to log in around midnight of 29 December 2014 <a href="/wiki/UTC" class="mw-redirect" title="UTC">UTC</a>.<sup id="cite_ref-6" class="reference"><a href="#cite_note-6"><span class="cite-bracket">[</span>2<span class="cite-bracket">]</span></a></sup> </p><p>The ISO week calendar relies on the <a href="/wiki/Gregorian_calendar" title="Gregorian calendar">Gregorian calendar</a>, which it augments, to define the new year day (Monday of week 01). As a result, extra weeks are spread across the 400-year cycle in a complex, seemingly random pattern. (However, a relatively simple algorithm to determine whether a year has 53 weeks from its ordinal number alone is shown under "Weeks per year" above.) Most <a href="/wiki/Calendar_reform" title="Calendar reform">calendar reform</a> proposals using <a href="/wiki/Leap_week_calendar" title="Leap week calendar">leap week designs</a> strive to simplify and harmonize this pattern, some by choosing a different <a href="/wiki/Leap_year" title="Leap year">leap cycle</a> (e.g. 293 years). </p><p>Not all parts of the world consider the week to begin with Monday. For example, in some Muslim countries, the normal work week begins on Saturday, while in Israel it begins on Sunday. In much of the Americas, although the work week is usually defined to start on Monday, the calendar week is often considered to start on Sunday. </p> <div class="mw-heading mw-heading2"><h2 id="Algorithms">Algorithms</h2><span class="mw-editsection"><span class="mw-editsection-bracket">[</span><a href="/w/index.php?title=ISO_week_date&action=edit&section=10" title="Edit section: Algorithms"><span>edit</span></a><span class="mw-editsection-bracket">]</span></span></div> <div class="mw-heading mw-heading3"><h3 id="Calculating_the_week_number_from_an_ordinal_date">Calculating the week number from an ordinal date</h3><span class="mw-editsection"><span class="mw-editsection-bracket">[</span><a href="/w/index.php?title=ISO_week_date&action=edit&section=11" title="Edit section: Calculating the week number from an ordinal date"><span>edit</span></a><span class="mw-editsection-bracket">]</span></span></div> <p>The week number (WW or <i>woy</i> for <i>week of year</i>) of any date can be calculated, given its <a href="/wiki/Ordinal_date" title="Ordinal date">ordinal date</a> (i.e. day of the year, <i>doy</i> or DDD, 1–365 or 366) and its <a href="/wiki/Day_of_the_week" class="mw-redirect" title="Day of the week">day of the week</a> (D or <i>dow</i>, 1–7). When using serial numbers for dates (e.g. in spreadsheets), <i>doy</i> is the serial number for a date minus the serial number for 31st December of the previous year, or alternatively minus the serial number for 1st January the same year plus one. </p> <dl><dt>Algorithm</dt></dl> <ol><li>Subtract the weekday number from the ordinal day of the year.</li> <li>Add 10.</li> <li><a href="/wiki/Division_(mathematics)#Of_integers" title="Division (mathematics)">Divide</a> by 7, discard the remainder. <ul><li>If the week number thus obtained equals 0, it means that the given date belongs to the preceding (week-based) year.</li> <li>If a week number of 53 is obtained, one must check that the date is not actually in week 1 of the following year.</li></ul></li></ol> <dl><dt>Formula</dt> <dd><span class="mwe-math-element"><span class="mwe-math-mathml-inline mwe-math-mathml-a11y" style="display: none;"><math xmlns="http://www.w3.org/1998/Math/MathML" alttext="{\displaystyle {\begin{aligned}y&={\text{year}}(date)\\w&=\left\lfloor {\frac {10+{\text{doy}}(date)-{\text{dow}}(date)}{7}}\right\rfloor \\{\text{woy}}(date)&={\begin{cases}{\text{weeks}}(y-1),&{\text{if }}w<1\\1,&{\text{if }}w>{\text{weeks}}(y)\\w,&{\text{otherwise.}}\end{cases}}\\{\text{woy}}(date)&\in [1,53]\\{\text{doy}}(date)&\in [1,366]\\{\text{dow}}(date)&\in [1,7]\\{\text{weeks}}(year)&\in [52,53]\\\end{aligned}}}"> <semantics> <mrow class="MJX-TeXAtom-ORD"> <mstyle displaystyle="true" scriptlevel="0"> <mrow class="MJX-TeXAtom-ORD"> <mtable columnalign="right left right left right left right left right left right left" rowspacing="3pt" columnspacing="0em 2em 0em 2em 0em 2em 0em 2em 0em 2em 0em" displaystyle="true"> <mtr> <mtd> <mi>y</mi> </mtd> <mtd> <mi></mi> <mo>=</mo> <mrow class="MJX-TeXAtom-ORD"> <mtext>year</mtext> </mrow> <mo stretchy="false">(</mo> <mi>d</mi> <mi>a</mi> <mi>t</mi> <mi>e</mi> <mo stretchy="false">)</mo> </mtd> </mtr> <mtr> <mtd> <mi>w</mi> </mtd> <mtd> <mi></mi> <mo>=</mo> <mrow> <mo>⌊</mo> <mrow class="MJX-TeXAtom-ORD"> <mfrac> <mrow> <mn>10</mn> <mo>+</mo> <mrow class="MJX-TeXAtom-ORD"> <mtext>doy</mtext> </mrow> <mo stretchy="false">(</mo> <mi>d</mi> <mi>a</mi> <mi>t</mi> <mi>e</mi> <mo stretchy="false">)</mo> <mo>−</mo> <mrow class="MJX-TeXAtom-ORD"> <mtext>dow</mtext> </mrow> <mo stretchy="false">(</mo> <mi>d</mi> <mi>a</mi> <mi>t</mi> <mi>e</mi> <mo stretchy="false">)</mo> </mrow> <mn>7</mn> </mfrac> </mrow> <mo>⌋</mo> </mrow> </mtd> </mtr> <mtr> <mtd> <mrow class="MJX-TeXAtom-ORD"> <mtext>woy</mtext> </mrow> <mo stretchy="false">(</mo> <mi>d</mi> <mi>a</mi> <mi>t</mi> <mi>e</mi> <mo stretchy="false">)</mo> </mtd> <mtd> <mi></mi> <mo>=</mo> <mrow class="MJX-TeXAtom-ORD"> <mrow> <mo>{</mo> <mtable columnalign="left left" rowspacing=".2em" columnspacing="1em" displaystyle="false"> <mtr> <mtd> <mrow class="MJX-TeXAtom-ORD"> <mtext>weeks</mtext> </mrow> <mo stretchy="false">(</mo> <mi>y</mi> <mo>−</mo> <mn>1</mn> <mo stretchy="false">)</mo> <mo>,</mo> </mtd> <mtd> <mrow class="MJX-TeXAtom-ORD"> <mtext>if </mtext> </mrow> <mi>w</mi> <mo><</mo> <mn>1</mn> </mtd> </mtr> <mtr> <mtd> <mn>1</mn> <mo>,</mo> </mtd> <mtd> <mrow class="MJX-TeXAtom-ORD"> <mtext>if </mtext> </mrow> <mi>w</mi> <mo>></mo> <mrow class="MJX-TeXAtom-ORD"> <mtext>weeks</mtext> </mrow> <mo stretchy="false">(</mo> <mi>y</mi> <mo stretchy="false">)</mo> </mtd> </mtr> <mtr> <mtd> <mi>w</mi> <mo>,</mo> </mtd> <mtd> <mrow class="MJX-TeXAtom-ORD"> <mtext>otherwise.</mtext> </mrow> </mtd> </mtr> </mtable> <mo fence="true" stretchy="true" symmetric="true"></mo> </mrow> </mrow> </mtd> </mtr> <mtr> <mtd> <mrow class="MJX-TeXAtom-ORD"> <mtext>woy</mtext> </mrow> <mo stretchy="false">(</mo> <mi>d</mi> <mi>a</mi> <mi>t</mi> <mi>e</mi> <mo stretchy="false">)</mo> </mtd> <mtd> <mi></mi> <mo>∈</mo> <mo stretchy="false">[</mo> <mn>1</mn> <mo>,</mo> <mn>53</mn> <mo stretchy="false">]</mo> </mtd> </mtr> <mtr> <mtd> <mrow class="MJX-TeXAtom-ORD"> <mtext>doy</mtext> </mrow> <mo stretchy="false">(</mo> <mi>d</mi> <mi>a</mi> <mi>t</mi> <mi>e</mi> <mo stretchy="false">)</mo> </mtd> <mtd> <mi></mi> <mo>∈</mo> <mo stretchy="false">[</mo> <mn>1</mn> <mo>,</mo> <mn>366</mn> <mo stretchy="false">]</mo> </mtd> </mtr> <mtr> <mtd> <mrow class="MJX-TeXAtom-ORD"> <mtext>dow</mtext> </mrow> <mo stretchy="false">(</mo> <mi>d</mi> <mi>a</mi> <mi>t</mi> <mi>e</mi> <mo stretchy="false">)</mo> </mtd> <mtd> <mi></mi> <mo>∈</mo> <mo stretchy="false">[</mo> <mn>1</mn> <mo>,</mo> <mn>7</mn> <mo stretchy="false">]</mo> </mtd> </mtr> <mtr> <mtd> <mrow class="MJX-TeXAtom-ORD"> <mtext>weeks</mtext> </mrow> <mo stretchy="false">(</mo> <mi>y</mi> <mi>e</mi> <mi>a</mi> <mi>r</mi> <mo stretchy="false">)</mo> </mtd> <mtd> <mi></mi> <mo>∈</mo> <mo stretchy="false">[</mo> <mn>52</mn> <mo>,</mo> <mn>53</mn> <mo stretchy="false">]</mo> </mtd> </mtr> </mtable> </mrow> </mstyle> </mrow> <annotation encoding="application/x-tex">{\displaystyle {\begin{aligned}y&={\text{year}}(date)\\w&=\left\lfloor {\frac {10+{\text{doy}}(date)-{\text{dow}}(date)}{7}}\right\rfloor \\{\text{woy}}(date)&={\begin{cases}{\text{weeks}}(y-1),&{\text{if }}w<1\\1,&{\text{if }}w>{\text{weeks}}(y)\\w,&{\text{otherwise.}}\end{cases}}\\{\text{woy}}(date)&\in [1,53]\\{\text{doy}}(date)&\in [1,366]\\{\text{dow}}(date)&\in [1,7]\\{\text{weeks}}(year)&\in [52,53]\\\end{aligned}}}</annotation> </semantics> </math></span><img src="https://wikimedia.org/api/rest_v1/media/math/render/svg/8d647370e96e762cb9240bde3948c7c77a1b3535" class="mwe-math-fallback-image-inline mw-invert skin-invert" aria-hidden="true" style="vertical-align: -14.55ex; margin-bottom: -0.288ex; width:50.258ex; height:30.843ex;" alt="{\displaystyle {\begin{aligned}y&={\text{year}}(date)\\w&=\left\lfloor {\frac {10+{\text{doy}}(date)-{\text{dow}}(date)}{7}}\right\rfloor \\{\text{woy}}(date)&={\begin{cases}{\text{weeks}}(y-1),&{\text{if }}w<1\\1,&{\text{if }}w>{\text{weeks}}(y)\\w,&{\text{otherwise.}}\end{cases}}\\{\text{woy}}(date)&\in [1,53]\\{\text{doy}}(date)&\in [1,366]\\{\text{dow}}(date)&\in [1,7]\\{\text{weeks}}(year)&\in [52,53]\\\end{aligned}}}"></span></dd></dl> <div class="mw-heading mw-heading3"><h3 id="Calculating_the_week_number_from_a_month_and_day_of_the_month">Calculating the week number from a month and day of the month</h3><span class="mw-editsection"><span class="mw-editsection-bracket">[</span><a href="/w/index.php?title=ISO_week_date&action=edit&section=12" title="Edit section: Calculating the week number from a month and day of the month"><span>edit</span></a><span class="mw-editsection-bracket">]</span></span></div> <p>If the ordinal date is not known, it can be computed from the month (MM or <i>moy</i>) and day of the month (DD or <i>dom</i>) by any of several methods; e.g. using a table such as the following. </p> <table class="wikitable"> <caption>Offset for the day of the month to get ordinal day of the year </caption> <tbody><tr> <th scope="row">Month </th> <th>Jan</th> <th>Feb</th> <th>Mar</th> <th>Apr</th> <th>May</th> <th>Jun</th> <th>Jul</th> <th>Aug</th> <th>Sep</th> <th>Oct</th> <th>Nov</th> <th>Dec</th> <th></th> <th>Add </th></tr> <tr> <th scope="row">Common year </th> <td rowspan="2">0</td> <td rowspan="2">31 </td> <td>59</td> <td>90</td> <td>120</td> <td>151</td> <td>181</td> <td>212</td> <td>243</td> <td>273</td> <td>304</td> <td>334</td> <td rowspan="2"></td> <td rowspan="2"><i>dom</i> </td></tr> <tr> <th scope="row">Leap year </th> <td>60</td> <td>91</td> <td>121</td> <td>152</td> <td>182</td> <td>213</td> <td>244</td> <td>274</td> <td>305</td> <td>335 </td></tr></tbody></table> <dl><dt>Example</dt> <dd>Find the week number of Saturday 5th November 2016 (leap year): <ul><li>Find the ordinal day number first:</li></ul></dd></dl> <pre><i>moy</i> = 11 <i>dom</i> = 5 <i>leap</i> = 1 <i>add</i> = 305, from table lookup <i>doy</i> = 305 + 5 = 310. </pre> <dl><dd><ul><li>Alternatively, use spreadsheet serial day numbers instead:</li></ul></dd></dl> <pre><i>off</i> = 42369, i.e. 31st December 2015 <i>day</i> = 42679 <i>doy</i> = 42679 − 42369 = 310. </pre> <dl><dd><ul><li>Finally, find the week number:</li></ul></dd></dl> <pre><i>dow</i> = 6, i.e. Saturday <i>woy</i> = (10 + 310 − 6) div 7 <i>woy</i> = (320 − 6) div 7 <i>woy</i> = 314 div 7 = 44. </pre> <div class="mw-heading mw-heading3"><h3 id="Calculating_an_ordinal_or_month_date_from_a_week_date">Calculating an ordinal or month date from a week date</h3><span class="mw-editsection"><span class="mw-editsection-bracket">[</span><a href="/w/index.php?title=ISO_week_date&action=edit&section=13" title="Edit section: Calculating an ordinal or month date from a week date"><span>edit</span></a><span class="mw-editsection-bracket">]</span></span></div> <dl><dt>Algorithm</dt></dl> <ol><li>Multiply the week number by 7.</li> <li>Then add the weekday number.</li> <li>From this sum subtract the correction for the year: <ul><li>Get the weekday of 4 January.</li> <li>Add 3.</li></ul></li> <li>The result is the ordinal date, which can be converted into a calendar date. <ul><li>If the ordinal date thus obtained is zero or negative, the date belongs to the previous calendar year;</li> <li>if it is greater than the number of days in the year, it belongs to the following year.</li></ul></li></ol> <dl><dt>Formula</dt> <dd><span class="mwe-math-element"><span class="mwe-math-mathml-inline mwe-math-mathml-a11y" style="display: none;"><math xmlns="http://www.w3.org/1998/Math/MathML" alttext="{\displaystyle {\begin{aligned}y&={\text{year}}(date)\\d&={\text{woy}}(date)\times 7+{\text{dow}}(date)-({\text{dow}}(y,1,4)+3)\\{\text{doy}}(date)&={\begin{cases}d+{\text{days}}(y-1),&{\text{if }}d<1\\d-{\text{days}}(y),&{\text{if }}d>{\text{days}}(y)\\d,&{\text{otherwise.}}\end{cases}}\\{\text{days}}(year)&\in [365,366]\\\end{aligned}}}"> <semantics> <mrow class="MJX-TeXAtom-ORD"> <mstyle displaystyle="true" scriptlevel="0"> <mrow class="MJX-TeXAtom-ORD"> <mtable columnalign="right left right left right left right left right left right left" rowspacing="3pt" columnspacing="0em 2em 0em 2em 0em 2em 0em 2em 0em 2em 0em" displaystyle="true"> <mtr> <mtd> <mi>y</mi> </mtd> <mtd> <mi></mi> <mo>=</mo> <mrow class="MJX-TeXAtom-ORD"> <mtext>year</mtext> </mrow> <mo stretchy="false">(</mo> <mi>d</mi> <mi>a</mi> <mi>t</mi> <mi>e</mi> <mo stretchy="false">)</mo> </mtd> </mtr> <mtr> <mtd> <mi>d</mi> </mtd> <mtd> <mi></mi> <mo>=</mo> <mrow class="MJX-TeXAtom-ORD"> <mtext>woy</mtext> </mrow> <mo stretchy="false">(</mo> <mi>d</mi> <mi>a</mi> <mi>t</mi> <mi>e</mi> <mo stretchy="false">)</mo> <mo>×</mo> <mn>7</mn> <mo>+</mo> <mrow class="MJX-TeXAtom-ORD"> <mtext>dow</mtext> </mrow> <mo stretchy="false">(</mo> <mi>d</mi> <mi>a</mi> <mi>t</mi> <mi>e</mi> <mo stretchy="false">)</mo> <mo>−</mo> <mo stretchy="false">(</mo> <mrow class="MJX-TeXAtom-ORD"> <mtext>dow</mtext> </mrow> <mo stretchy="false">(</mo> <mi>y</mi> <mo>,</mo> <mn>1</mn> <mo>,</mo> <mn>4</mn> <mo stretchy="false">)</mo> <mo>+</mo> <mn>3</mn> <mo stretchy="false">)</mo> </mtd> </mtr> <mtr> <mtd> <mrow class="MJX-TeXAtom-ORD"> <mtext>doy</mtext> </mrow> <mo stretchy="false">(</mo> <mi>d</mi> <mi>a</mi> <mi>t</mi> <mi>e</mi> <mo stretchy="false">)</mo> </mtd> <mtd> <mi></mi> <mo>=</mo> <mrow class="MJX-TeXAtom-ORD"> <mrow> <mo>{</mo> <mtable columnalign="left left" rowspacing=".2em" columnspacing="1em" displaystyle="false"> <mtr> <mtd> <mi>d</mi> <mo>+</mo> <mrow class="MJX-TeXAtom-ORD"> <mtext>days</mtext> </mrow> <mo stretchy="false">(</mo> <mi>y</mi> <mo>−</mo> <mn>1</mn> <mo stretchy="false">)</mo> <mo>,</mo> </mtd> <mtd> <mrow class="MJX-TeXAtom-ORD"> <mtext>if </mtext> </mrow> <mi>d</mi> <mo><</mo> <mn>1</mn> </mtd> </mtr> <mtr> <mtd> <mi>d</mi> <mo>−</mo> <mrow class="MJX-TeXAtom-ORD"> <mtext>days</mtext> </mrow> <mo stretchy="false">(</mo> <mi>y</mi> <mo stretchy="false">)</mo> <mo>,</mo> </mtd> <mtd> <mrow class="MJX-TeXAtom-ORD"> <mtext>if </mtext> </mrow> <mi>d</mi> <mo>></mo> <mrow class="MJX-TeXAtom-ORD"> <mtext>days</mtext> </mrow> <mo stretchy="false">(</mo> <mi>y</mi> <mo stretchy="false">)</mo> </mtd> </mtr> <mtr> <mtd> <mi>d</mi> <mo>,</mo> </mtd> <mtd> <mrow class="MJX-TeXAtom-ORD"> <mtext>otherwise.</mtext> </mrow> </mtd> </mtr> </mtable> <mo fence="true" stretchy="true" symmetric="true"></mo> </mrow> </mrow> </mtd> </mtr> <mtr> <mtd> <mrow class="MJX-TeXAtom-ORD"> <mtext>days</mtext> </mrow> <mo stretchy="false">(</mo> <mi>y</mi> <mi>e</mi> <mi>a</mi> <mi>r</mi> <mo stretchy="false">)</mo> </mtd> <mtd> <mi></mi> <mo>∈</mo> <mo stretchy="false">[</mo> <mn>365</mn> <mo>,</mo> <mn>366</mn> <mo stretchy="false">]</mo> </mtd> </mtr> </mtable> </mrow> </mstyle> </mrow> <annotation encoding="application/x-tex">{\displaystyle {\begin{aligned}y&={\text{year}}(date)\\d&={\text{woy}}(date)\times 7+{\text{dow}}(date)-({\text{dow}}(y,1,4)+3)\\{\text{doy}}(date)&={\begin{cases}d+{\text{days}}(y-1),&{\text{if }}d<1\\d-{\text{days}}(y),&{\text{if }}d>{\text{days}}(y)\\d,&{\text{otherwise.}}\end{cases}}\\{\text{days}}(year)&\in [365,366]\\\end{aligned}}}</annotation> </semantics> </math></span><img src="https://wikimedia.org/api/rest_v1/media/math/render/svg/9445d079f48167e16fd12daa2c8bddf5d5af3f1a" class="mwe-math-fallback-image-inline mw-invert skin-invert" aria-hidden="true" style="vertical-align: -8.505ex; width:62.319ex; height:18.176ex;" alt="{\displaystyle {\begin{aligned}y&={\text{year}}(date)\\d&={\text{woy}}(date)\times 7+{\text{dow}}(date)-({\text{dow}}(y,1,4)+3)\\{\text{doy}}(date)&={\begin{cases}d+{\text{days}}(y-1),&{\text{if }}d<1\\d-{\text{days}}(y),&{\text{if }}d>{\text{days}}(y)\\d,&{\text{otherwise.}}\end{cases}}\\{\text{days}}(year)&\in [365,366]\\\end{aligned}}}"></span></dd></dl> <div class="mw-heading mw-heading2"><h2 id="Other_week_numbering_systems">Other week numbering systems</h2><span class="mw-editsection"><span class="mw-editsection-bracket">[</span><a href="/w/index.php?title=ISO_week_date&action=edit&section=14" title="Edit section: Other week numbering systems"><span>edit</span></a><span class="mw-editsection-bracket">]</span></span></div> <link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1236090951"><div role="note" class="hatnote navigation-not-searchable">Main articles: <a href="/wiki/Week#Other_week_numbering_systems" title="Week">Week § Other week numbering systems</a>, and <a href="/wiki/Week_number" class="mw-redirect" title="Week number">week number</a></div> <p>The US system has weeks from Sunday through Saturday, and partial weeks at the beginning and the end of the year, i.e. 52 full and 1 partial week of 1 or 2 days if the year starts on Sunday or ends on Saturday, 52 full and 2 single-day weeks if a leap year starts on Saturday and ends on Sunday, otherwise 51 full and 2 partial weeks. An advantage is that no separate year numbering like the ISO year is needed. Correspondence of <a href="/wiki/Lexicographical_order" class="mw-redirect" title="Lexicographical order">lexicographical order</a> and chronological order is preserved (just like with the ISO year-week-weekday numbering), but partial weeks make some computations of weekly statistics or payments inaccurate at the end of December or the beginning of January or both. </p><p>The US <a href="/wiki/Broadcast_calendar" title="Broadcast calendar">broadcast calendar</a> designates the week containing 1 January (and starting Monday) as the first of the year, but otherwise works like ISO week numbering without partial weeks. Up to six days of the previous December may be part of the first week of the year. </p><p>A mix of those, wherein weeks start Sunday and "containing 1 January" defines the first week, is used in US accounting, resulting in a system with years having also 52 or 53 weeks. </p> <div class="mw-heading mw-heading2"><h2 id="References">References</h2><span class="mw-editsection"><span class="mw-editsection-bracket">[</span><a href="/w/index.php?title=ISO_week_date&action=edit&section=15" title="Edit section: References"><span>edit</span></a><span class="mw-editsection-bracket">]</span></span></div> <link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1239543626"><div class="reflist"> <div class="mw-references-wrap"><ol class="references"> <li id="cite_note-Gent3-5"><span class="mw-cite-backlink"><b><a href="#cite_ref-Gent3_5-0">^</a></b></span> <span class="reference-text"><style data-mw-deduplicate="TemplateStyles:r1238218222">.mw-parser-output cite.citation{font-style:inherit;word-wrap:break-word}.mw-parser-output .citation q{quotes:"\"""\"""'""'"}.mw-parser-output .citation:target{background-color:rgba(0,127,255,0.133)}.mw-parser-output .id-lock-free.id-lock-free a{background:url("//upload.wikimedia.org/wikipedia/commons/6/65/Lock-green.svg")right 0.1em center/9px no-repeat}.mw-parser-output .id-lock-limited.id-lock-limited a,.mw-parser-output .id-lock-registration.id-lock-registration a{background:url("//upload.wikimedia.org/wikipedia/commons/d/d6/Lock-gray-alt-2.svg")right 0.1em center/9px no-repeat}.mw-parser-output .id-lock-subscription.id-lock-subscription a{background:url("//upload.wikimedia.org/wikipedia/commons/a/aa/Lock-red-alt-2.svg")right 0.1em center/9px no-repeat}.mw-parser-output .cs1-ws-icon a{background:url("//upload.wikimedia.org/wikipedia/commons/4/4c/Wikisource-logo.svg")right 0.1em center/12px no-repeat}body:not(.skin-timeless):not(.skin-minerva) .mw-parser-output .id-lock-free a,body:not(.skin-timeless):not(.skin-minerva) .mw-parser-output .id-lock-limited a,body:not(.skin-timeless):not(.skin-minerva) .mw-parser-output .id-lock-registration a,body:not(.skin-timeless):not(.skin-minerva) .mw-parser-output .id-lock-subscription a,body:not(.skin-timeless):not(.skin-minerva) .mw-parser-output .cs1-ws-icon a{background-size:contain;padding:0 1em 0 0}.mw-parser-output .cs1-code{color:inherit;background:inherit;border:none;padding:inherit}.mw-parser-output .cs1-hidden-error{display:none;color:var(--color-error,#d33)}.mw-parser-output .cs1-visible-error{color:var(--color-error,#d33)}.mw-parser-output .cs1-maint{display:none;color:#085;margin-left:0.3em}.mw-parser-output .cs1-kern-left{padding-left:0.2em}.mw-parser-output .cs1-kern-right{padding-right:0.2em}.mw-parser-output .citation .mw-selflink{font-weight:inherit}@media screen{.mw-parser-output .cs1-format{font-size:95%}html.skin-theme-clientpref-night .mw-parser-output .cs1-maint{color:#18911f}}@media screen and (prefers-color-scheme:dark){html.skin-theme-clientpref-os .mw-parser-output .cs1-maint{color:#18911f}}</style><cite id="CITEREFGent" class="citation web cs1">Gent, Robert H. <a rel="nofollow" class="external text" href="http://www.staff.science.uu.nl/~gent0113/calendar/isocalendar.htm">"The Mathematics of the ISO 8601 Calendar"</a>. <a rel="nofollow" class="external text" href="https://web.archive.org/web/20181224200200/http://www.staff.science.uu.nl/~gent0113/calendar/isocalendar.htm%20">Archived</a> from the original on 2018-12-24<span class="reference-accessdate">. Retrieved <span class="nowrap">2011-08-17</span></span>.</cite><span title="ctx_ver=Z39.88-2004&rft_val_fmt=info%3Aofi%2Ffmt%3Akev%3Amtx%3Abook&rft.genre=unknown&rft.btitle=The+Mathematics+of+the+ISO+8601+Calendar&rft.aulast=Gent&rft.aufirst=Robert+H.&rft_id=http%3A%2F%2Fwww.staff.science.uu.nl%2F~gent0113%2Fcalendar%2Fisocalendar.htm&rfr_id=info%3Asid%2Fen.wikipedia.org%3AISO+week+date" class="Z3988"></span></span> </li> <li id="cite_note-6"><span class="mw-cite-backlink"><b><a href="#cite_ref-6">^</a></b></span> <span class="reference-text"><link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1238218222"><cite class="citation news cs1"><a rel="nofollow" class="external text" href="https://www.theguardian.com/technology/2014/dec/29/twitter-2015-date-bug">"Twitter kicks Android app users out for five hours due to 2015 date bug"</a>. <i>the Guardian</i>. 29 December 2014.</cite><span title="ctx_ver=Z39.88-2004&rft_val_fmt=info%3Aofi%2Ffmt%3Akev%3Amtx%3Ajournal&rft.genre=article&rft.jtitle=the+Guardian&rft.atitle=Twitter+kicks+Android+app+users+out+for+five+hours+due+to+2015+date+bug&rft.date=2014-12-29&rft_id=https%3A%2F%2Fwww.theguardian.com%2Ftechnology%2F2014%2Fdec%2F29%2Ftwitter-2015-date-bug&rfr_id=info%3Asid%2Fen.wikipedia.org%3AISO+week+date" class="Z3988"></span></span> </li> </ol></div></div> <div class="mw-heading mw-heading2"><h2 id="External_links">External links</h2><span class="mw-editsection"><span class="mw-editsection-bracket">[</span><a href="/w/index.php?title=ISO_week_date&action=edit&section=16" title="Edit section: External links"><span>edit</span></a><span class="mw-editsection-bracket">]</span></span></div> <ul><li><a rel="nofollow" class="external text" href="https://webspace.science.uu.nl/~gent0113/calendar/isocalendar.htm">The Mathematics of the ISO 8601 Calendar</a></li> <li><a rel="nofollow" class="external text" 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measurement</a> and <a href="/wiki/Time_standard" title="Time standard">standards</a></div></th></tr><tr><td class="navbox-abovebelow" colspan="3"><div> <ul><li><a href="/wiki/Chronometry" title="Chronometry">Chronometry</a></li> <li><a href="/wiki/Orders_of_magnitude_(time)" title="Orders of magnitude (time)">Orders of magnitude</a></li> <li><a href="/wiki/Time_metrology" class="mw-redirect" title="Time metrology">Metrology</a></li></ul> </div></td></tr><tr><th scope="row" class="navbox-group" style="width:1%">International standards</th><td class="navbox-list-with-group navbox-list navbox-odd" style="width:100%;padding:0"><div style="padding:0 0.25em"> <ul><li><a href="/wiki/Coordinated_Universal_Time" title="Coordinated Universal Time">Coordinated Universal Time</a> <ul><li><a href="/wiki/UTC_offset" title="UTC offset">offset</a></li></ul></li> <li><a href="/wiki/Universal_Time" title="Universal Time">UT</a></li> <li><a href="/wiki/%CE%94T_(timekeeping)" title="ΔT (timekeeping)">ΔT</a></li> <li><a href="/wiki/DUT1" title="DUT1">DUT1</a></li> <li><a href="/wiki/International_Earth_Rotation_and_Reference_Systems_Service" title="International Earth Rotation and Reference Systems Service">International Earth Rotation and Reference Systems Service</a></li> <li><a href="/wiki/ISO_31-1" title="ISO 31-1">ISO 31-1</a></li> <li><a href="/wiki/ISO_8601" title="ISO 8601">ISO 8601</a></li> <li><a href="/wiki/International_Atomic_Time" title="International Atomic Time">International Atomic Time</a></li> <li><a href="/wiki/12-hour_clock" title="12-hour clock">12-hour clock</a></li> <li><a href="/wiki/24-hour_clock" title="24-hour clock">24-hour clock</a></li> <li><a href="/wiki/Barycentric_Coordinate_Time" title="Barycentric Coordinate Time">Barycentric Coordinate Time</a></li> <li><a href="/wiki/Barycentric_Dynamical_Time" title="Barycentric Dynamical Time">Barycentric Dynamical Time</a></li> <li><a href="/wiki/Civil_time" title="Civil time">Civil time</a></li> <li><a href="/wiki/Daylight_saving_time" title="Daylight saving time">Daylight saving time</a></li> <li><a href="/wiki/Geocentric_Coordinate_Time" title="Geocentric Coordinate Time">Geocentric Coordinate Time</a></li> <li><a href="/wiki/International_Date_Line" title="International Date Line">International Date Line</a></li> <li><a href="/wiki/IERS_Reference_Meridian" title="IERS Reference Meridian">IERS Reference Meridian</a></li> <li><a href="/wiki/Leap_second" title="Leap second">Leap second</a></li> <li><a href="/wiki/Solar_time" title="Solar time">Solar time</a></li> <li><a href="/wiki/Terrestrial_Time" title="Terrestrial Time">Terrestrial Time</a></li> <li><a href="/wiki/Time_zone" title="Time zone">Time zone</a></li> <li><a href="/wiki/180th_meridian" title="180th meridian">180th meridian</a></li></ul> </div></td><td class="noviewer navbox-image" rowspan="9" style="width:1px;padding:0 0 0 2px"><div><span typeof="mw:File"><a href="/wiki/Hourglass" 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srcset="//upload.wikimedia.org/wikipedia/commons/thumb/6/63/Aleutian_Islands_with_180th_meridian_and_International_Date_Line_%28cropped%29.png/113px-Aleutian_Islands_with_180th_meridian_and_International_Date_Line_%28cropped%29.png 1.5x, //upload.wikimedia.org/wikipedia/commons/thumb/6/63/Aleutian_Islands_with_180th_meridian_and_International_Date_Line_%28cropped%29.png/150px-Aleutian_Islands_with_180th_meridian_and_International_Date_Line_%28cropped%29.png 2x" data-file-width="496" data-file-height="1007" /></a></span></div></td></tr><tr><th scope="row" class="navbox-group" style="width:1%">Obsolete standards</th><td class="navbox-list-with-group navbox-list navbox-even" style="width:100%;padding:0"><div style="padding:0 0.25em"> <ul><li><a href="/wiki/Ephemeris_time" title="Ephemeris time">Ephemeris time</a></li> <li><a href="/wiki/Greenwich_Mean_Time" title="Greenwich Mean Time">Greenwich Mean Time</a></li> <li><a href="/wiki/Prime_meridian" title="Prime meridian">Prime meridian</a></li></ul> </div></td></tr><tr><th scope="row" class="navbox-group" style="width:1%"><a href="/wiki/Time_in_physics" title="Time in physics">Time in physics</a></th><td class="navbox-list-with-group navbox-list navbox-odd" style="width:100%;padding:0"><div style="padding:0 0.25em"> <ul><li><a href="/wiki/Absolute_space_and_time" title="Absolute space and time">Absolute space and time</a></li> <li><a href="/wiki/Spacetime" title="Spacetime">Spacetime</a></li> <li><a href="/wiki/Chronon" title="Chronon">Chronon</a></li> <li><a href="/wiki/Continuous_signal" class="mw-redirect" title="Continuous signal">Continuous signal</a></li> <li><a href="/wiki/Coordinate_time" title="Coordinate time">Coordinate time</a></li> <li><a href="/wiki/Cosmological_decade" title="Cosmological decade">Cosmological decade</a></li> <li><a href="/wiki/Discrete_time_and_continuous_time" title="Discrete time and continuous time">Discrete time and continuous time</a></li> <li><a href="/wiki/Proper_time" title="Proper time">Proper time</a></li> <li><a href="/wiki/Theory_of_relativity" title="Theory of relativity">Theory of relativity</a></li> <li><a href="/wiki/Time_dilation" title="Time dilation">Time dilation</a></li> <li><a href="/wiki/Gravitational_time_dilation" title="Gravitational time dilation">Gravitational time dilation</a></li> <li><a href="/wiki/Time_domain" title="Time domain">Time domain</a></li> <li><a href="/wiki/Time-translation_symmetry" title="Time-translation symmetry">Time-translation symmetry</a></li> <li><a href="/wiki/T-symmetry" title="T-symmetry">T-symmetry</a></li></ul> </div></td></tr><tr><th scope="row" class="navbox-group" style="width:1%"><a href="/wiki/Horology" class="mw-redirect" title="Horology">Horology</a></th><td class="navbox-list-with-group navbox-list navbox-even" style="width:100%;padding:0"><div style="padding:0 0.25em"> <ul><li><a href="/wiki/Clock" title="Clock">Clock</a></li> <li><a href="/wiki/Astrarium" title="Astrarium">Astrarium</a></li> <li><a href="/wiki/Atomic_clock" title="Atomic clock">Atomic clock</a></li> <li><a href="/wiki/Complication_(horology)" title="Complication (horology)">Complication</a></li> <li><a href="/wiki/History_of_timekeeping_devices" title="History of timekeeping devices">History of timekeeping devices</a></li> <li><a href="/wiki/Hourglass" title="Hourglass">Hourglass</a></li> <li><a href="/wiki/Marine_chronometer" title="Marine chronometer">Marine chronometer</a></li> <li><a href="/wiki/Marine_sandglass" title="Marine sandglass">Marine sandglass</a></li> <li><a href="/wiki/Radio_clock" title="Radio clock">Radio clock</a></li> <li><a href="/wiki/Watch" title="Watch">Watch</a> <ul><li><a href="/wiki/Stopwatch" title="Stopwatch">stopwatch</a></li></ul></li> <li><a href="/wiki/Water_clock" title="Water clock">Water clock</a></li> <li><a href="/wiki/Sundial" title="Sundial">Sundial</a></li> <li><a href="/wiki/Dialing_scales" title="Dialing scales">Dialing scales</a></li> <li><a href="/wiki/Equation_of_time" title="Equation of time">Equation of time</a></li> <li><a href="/wiki/History_of_sundials" title="History of sundials">History of sundials</a></li> <li><a href="/wiki/Schema_for_horizontal_dials" title="Schema for horizontal dials">Sundial markup schema</a></li></ul> </div></td></tr><tr><th scope="row" class="navbox-group" style="width:1%"><a href="/wiki/Calendar" title="Calendar">Calendar</a></th><td class="navbox-list-with-group navbox-list navbox-odd" style="width:100%;padding:0"><div style="padding:0 0.25em"> <ul><li><a href="/wiki/Gregorian_calendar" title="Gregorian calendar">Gregorian</a></li> <li><a href="/wiki/Hebrew_calendar" title="Hebrew calendar">Hebrew</a></li> <li><a href="/wiki/Hindu_calendar" title="Hindu calendar">Hindu</a></li> <li><a href="/wiki/Holocene_calendar" title="Holocene calendar">Holocene</a></li> <li><a href="/wiki/Islamic_calendar" title="Islamic calendar">Islamic</a> (lunar Hijri)</li> <li><a href="/wiki/Julian_calendar" title="Julian calendar">Julian</a></li> <li><a href="/wiki/Solar_Hijri_calendar" title="Solar Hijri calendar">Solar Hijri</a></li> <li><a href="/wiki/Astronomical_year_numbering" title="Astronomical year numbering">Astronomical</a></li> <li><a href="/wiki/Dominical_letter" title="Dominical letter">Dominical letter</a></li> <li><a href="/wiki/Epact" title="Epact">Epact</a></li> <li><a href="/wiki/Equinox" title="Equinox">Equinox</a></li> <li><a href="/wiki/Intercalation_(timekeeping)" title="Intercalation (timekeeping)">Intercalation</a></li> <li><a href="/wiki/Julian_day" title="Julian day">Julian day</a></li> <li><a href="/wiki/Leap_year" title="Leap year">Leap year</a></li> <li><a href="/wiki/Lunar_calendar" title="Lunar calendar">Lunar</a></li> <li><a href="/wiki/Lunisolar_calendar" title="Lunisolar calendar">Lunisolar</a></li> <li><a href="/wiki/Solar_calendar" title="Solar calendar">Solar</a></li> <li><a href="/wiki/Solstice" title="Solstice">Solstice</a></li> <li><a href="/wiki/Tropical_year" title="Tropical year">Tropical year</a></li> <li><a href="/wiki/Determination_of_the_day_of_the_week" title="Determination of the day of the week">Weekday determination</a></li> <li><a href="/wiki/Names_of_the_days_of_the_week" title="Names of the days of the week">Weekday names</a></li></ul> </div></td></tr><tr><th scope="row" class="navbox-group" style="width:1%">Archaeology and geology</th><td class="navbox-list-with-group navbox-list navbox-even" style="width:100%;padding:0"><div style="padding:0 0.25em"> <ul><li><a href="/wiki/Chronological_dating" title="Chronological dating">Chronological dating</a></li> <li><a href="/wiki/Geologic_time_scale" title="Geologic time scale">Geologic time scale</a></li> <li><a href="/wiki/International_Commission_on_Stratigraphy" title="International Commission on Stratigraphy">International Commission on Stratigraphy</a></li></ul> </div></td></tr><tr><th scope="row" class="navbox-group" style="width:1%"><a href="/wiki/Astronomical_chronology" title="Astronomical chronology">Astronomical chronology</a></th><td class="navbox-list-with-group navbox-list navbox-odd" style="width:100%;padding:0"><div style="padding:0 0.25em"> <ul><li><a href="/wiki/Galactic_year" title="Galactic year">Galactic year</a></li> <li><a href="/wiki/Nuclear_timescale" title="Nuclear timescale">Nuclear timescale</a></li> <li><a href="/wiki/Precession" title="Precession">Precession</a></li> <li><a href="/wiki/Sidereal_time" title="Sidereal time">Sidereal time</a></li></ul> </div></td></tr><tr><th scope="row" class="navbox-group" style="width:1%">Other <a href="/wiki/Unit_of_time" title="Unit of time">units of time</a></th><td class="navbox-list-with-group navbox-list navbox-even" style="width:100%;padding:0"><div style="padding:0 0.25em"> <ul><li><a href="/wiki/Instant" title="Instant">Instant</a></li> <li><a href="/wiki/Flick_(time)" title="Flick (time)">Flick</a></li> <li><a href="/wiki/Shake_(unit)" title="Shake (unit)">Shake</a></li> <li><a href="/wiki/Jiffy_(time)" title="Jiffy (time)">Jiffy</a></li> <li><a href="/wiki/Second" title="Second">Second</a></li> <li><a href="/wiki/Minute" title="Minute">Minute</a></li> <li><a href="/wiki/Moment_(unit)" title="Moment (unit)">Moment</a></li> <li><a href="/wiki/Hour" title="Hour">Hour</a></li> <li><a href="/wiki/Day" title="Day">Day</a></li> <li><a href="/wiki/Week" title="Week">Week</a></li> <li><a href="/wiki/Fortnight" title="Fortnight">Fortnight</a></li> <li><a href="/wiki/Month" title="Month">Month</a></li> <li><a href="/wiki/Year" title="Year">Year</a></li> <li><a href="/wiki/Olympiad" title="Olympiad">Olympiad</a></li> <li><a href="/wiki/Lustrum" title="Lustrum">Lustrum</a></li> <li><a href="/wiki/Decade" title="Decade">Decade</a></li> <li><a href="/wiki/Century" title="Century">Century</a></li> <li><a href="/wiki/Saeculum" title="Saeculum">Saeculum</a></li> <li><a href="/wiki/Millennium" title="Millennium">Millennium</a></li></ul> </div></td></tr><tr><th scope="row" class="navbox-group" style="width:1%">Related topics</th><td class="navbox-list-with-group navbox-list navbox-odd" style="width:100%;padding:0"><div style="padding:0 0.25em"> <ul><li><a href="/wiki/Chronology" title="Chronology">Chronology</a></li> <li><a href="/wiki/Duration_(philosophy)" title="Duration (philosophy)">Duration</a> <ul><li><a href="/wiki/Duration_(music)" title="Duration (music)">music</a></li></ul></li> <li><a href="/wiki/Mental_chronometry" title="Mental chronometry">Mental chronometry</a></li> <li><a href="/wiki/Decimal_time" title="Decimal time">Decimal time</a></li> <li><a href="/wiki/Metric_time" title="Metric time">Metric time</a></li> <li><a href="/wiki/System_time" title="System time">System time</a></li> <li><a href="/wiki/Time_metrology" class="mw-redirect" title="Time metrology">Time metrology</a></li> <li><a href="/wiki/Time_value_of_money" title="Time value of money">Time value of money</a></li> <li><a href="/wiki/Timekeeper" title="Timekeeper">Timekeeper</a></li></ul> </div></td></tr></tbody></table></div> <div class="navbox-styles"><link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1129693374"><link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1236075235"><link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1129693374"></div><div role="navigation" class="navbox" aria-labelledby="Chronology" style="padding:3px"><table class="nowraplinks mw-collapsible mw-collapsed navbox-inner" style="border-spacing:0;background:transparent;color:inherit"><tbody><tr><th scope="col" class="navbox-title" colspan="2"><link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1129693374"><link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1239400231"><div class="navbar plainlinks hlist navbar-mini"><ul><li class="nv-view"><a href="/wiki/Template:Chronology" title="Template:Chronology"><abbr title="View this template">v</abbr></a></li><li class="nv-talk"><a href="/wiki/Template_talk:Chronology" title="Template talk:Chronology"><abbr title="Discuss this template">t</abbr></a></li><li class="nv-edit"><a href="/wiki/Special:EditPage/Template:Chronology" title="Special:EditPage/Template:Chronology"><abbr title="Edit this template">e</abbr></a></li></ul></div><div id="Chronology" style="font-size:114%;margin:0 4em"><a href="/wiki/Chronology" title="Chronology">Chronology</a></div></th></tr><tr><th scope="row" class="navbox-group" style="width:1%;line-height:1.2em;background:#cc9;">Key topics</th><td class="navbox-list-with-group navbox-list navbox-odd hlist" style="width:100%;padding:0"><div style="padding:0 0.25em"> <ul><li><a href="/wiki/Archaeology" title="Archaeology">Archaeology</a></li> <li><a href="/wiki/Astronomy" title="Astronomy">Astronomy</a></li> <li><a href="/wiki/Geology" title="Geology">Geology</a></li> <li><a href="/wiki/History" title="History">History</a> <ul><li><a href="/wiki/Big_History" title="Big History">Big History</a></li></ul></li> <li><a href="/wiki/Paleontology" title="Paleontology">Paleontology</a></li> <li><a href="/wiki/Time" title="Time">Time</a></li></ul> </div></td></tr><tr><th scope="row" class="navbox-group" style="width:1%;line-height:1.2em;background:#cc9;"><div class="hlist"><ul><li><a href="/wiki/Periodization" title="Periodization">Periods</a></li><li><a href="/wiki/Era" title="Era">Eras</a></li><li><a href="/wiki/Epoch_(reference_date)" class="mw-redirect" title="Epoch (reference date)">Epochs</a></li></ul></div></th><td class="navbox-list-with-group navbox-list navbox-odd hlist" style="width:100%;padding:0"><div style="padding:0 0.25em"></div><table class="nowraplinks navbox-subgroup" style="border-spacing:0"><tbody><tr><th scope="row" class="navbox-group" style="width:8.0em;font-weight:normal;background:#cc9;"><a href="/wiki/Calendar_era" title="Calendar era">Calendar eras</a></th><td class="navbox-list-with-group navbox-list navbox-even" style="padding:0"><div style="padding:0 0.25em"> <ul><li><a href="/wiki/Holocene_calendar" title="Holocene calendar">Human Era</a></li> <li><i><a href="/wiki/Ab_urbe_condita" title="Ab urbe condita">Ab urbe condita</a></i></li> <li><a href="/wiki/Anno_Domini" title="Anno Domini">Anno Domini</a> / <a href="/wiki/Common_Era" title="Common Era">Common Era</a></li> <li><a href="/wiki/Anno_Mundi" title="Anno Mundi">Anno Mundi</a></li> <li><a href="/wiki/Bosporan_era" title="Bosporan era">Bosporan era</a></li> <li><a href="/wiki/Bostran_era" title="Bostran era">Bostran era</a></li> <li><a href="/wiki/Byzantine_calendar" title="Byzantine calendar">Byzantine era</a></li> <li><a href="/wiki/Seleucid_era" title="Seleucid era">Seleucid era</a></li> <li><a href="/wiki/Era_of_Caesar_(Iberian_Peninsula)" class="mw-redirect" title="Era of Caesar (Iberian Peninsula)">Era of Caesar (Iberia)</a></li> <li><a href="/wiki/Before_present" class="mw-redirect" title="Before present">Before present</a></li> <li><a href="/wiki/Islamic_calendar" title="Islamic calendar">Hijri</a></li> <li><a href="/wiki/Egyptian_chronology" title="Egyptian chronology">Egyptian</a></li> <li><a href="/wiki/Sothic_cycle" title="Sothic cycle">Sothic cycle</a></li> <li><a href="/wiki/Hindu_units_of_time" title="Hindu units of time">Hindu units of time</a> (<a href="/wiki/Yuga" title="Yuga">Yuga</a>)</li> <li><a href="/wiki/Mesoamerican_calendars" title="Mesoamerican calendars">Mesoamerican</a> <ul><li><a href="/wiki/Mesoamerican_Long_Count_calendar" title="Mesoamerican Long Count calendar">Long Count</a></li> <li><a href="/wiki/Maya_calendar#Short_Count" title="Maya calendar">Short Count</a></li> <li><a href="/wiki/Tzolk%27in" class="mw-redirect" title="Tzolk'in">Tzolk'in</a></li> <li><a href="/wiki/Haab%27" class="mw-redirect" title="Haab'">Haab'</a></li></ul></li></ul> </div></td></tr><tr><th scope="row" class="navbox-group" style="width:8.0em;font-weight:normal;background:#cc9;"><a href="/wiki/Regnal_year" title="Regnal year">Regnal year</a></th><td class="navbox-list-with-group navbox-list navbox-odd" style="padding:0"><div style="padding:0 0.25em"> <ul><li><a href="/wiki/Anka_year" title="Anka year">Anka year</a></li> <li><a href="/wiki/Canon_of_Kings" title="Canon of Kings">Canon of Kings</a></li> <li><a href="/wiki/Regnal_years_of_English_and_British_monarchs" title="Regnal years of English and British monarchs">English and British regnal year</a></li> <li><a href="/wiki/Category:Regnal_lists" title="Category:Regnal lists">Lists of kings</a></li> <li><a href="/wiki/Limmu" title="Limmu">Limmu</a></li></ul> </div></td></tr><tr><th scope="row" class="navbox-group" style="width:8.0em;font-weight:normal;background:#cc9;"><a href="/wiki/Regnal_year" title="Regnal year">Era names</a></th><td class="navbox-list-with-group navbox-list navbox-even" style="padding:0"><div style="padding:0 0.25em"> <ul><li><a href="/wiki/Chinese_era_name" title="Chinese era name">Chinese</a></li> <li><a href="/wiki/Japanese_era_name" title="Japanese era name">Japanese</a></li> <li><a href="/wiki/Korean_era_name" title="Korean era name">Korean</a></li> <li><a href="/wiki/Vietnamese_era_name" title="Vietnamese era name">Vietnamese</a></li></ul> </div></td></tr></tbody></table><div></div></td></tr><tr><th scope="row" class="navbox-group" style="width:1%;line-height:1.2em;background:#cc9;"><a href="/wiki/Calendar" title="Calendar">Calendars</a></th><td class="navbox-list-with-group navbox-list navbox-odd hlist" style="width:100%;padding:0"><div style="padding:0 0.25em"></div><table class="nowraplinks navbox-subgroup" style="border-spacing:0"><tbody><tr><th scope="row" class="navbox-group" style="width:8.0em;font-weight:normal;background:#cc9;">Pre-Julian / Julian</th><td class="navbox-list-with-group navbox-list navbox-odd" style="padding:0"><div style="padding:0 0.25em"> <ul><li><a href="/wiki/Roman_calendar" title="Roman calendar">Pre-Julian Roman</a></li> <li><a href="/wiki/Julian_calendar" title="Julian calendar">Original Julian</a></li> <li><a href="/wiki/Proleptic_Julian_calendar" title="Proleptic Julian calendar">Proleptic Julian</a></li> <li><a href="/wiki/Revised_Julian_calendar" title="Revised Julian calendar">Revised Julian</a></li></ul> </div></td></tr><tr><th scope="row" class="navbox-group" style="width:8.0em;font-weight:normal;background:#cc9;">Gregorian</th><td class="navbox-list-with-group navbox-list navbox-even" style="padding:0"><div style="padding:0 0.25em"> <ul><li><a href="/wiki/Gregorian_calendar" title="Gregorian calendar">Gregorian</a></li> <li><a href="/wiki/Proleptic_Gregorian_calendar" title="Proleptic Gregorian calendar">Proleptic Gregorian</a></li> <li><a href="/wiki/Old_Style_and_New_Style_dates" title="Old Style and New Style dates">Old Style and New Style dates</a></li> <li><a href="/wiki/Adoption_of_the_Gregorian_calendar" title="Adoption of the Gregorian calendar">Adoption of the Gregorian calendar</a></li> <li><a href="/wiki/Dual_dating" title="Dual dating">Dual dating</a></li></ul> </div></td></tr><tr><th scope="row" class="navbox-group" style="width:8.0em;font-weight:normal;background:#cc9;">Astronomical</th><td class="navbox-list-with-group navbox-list navbox-odd" style="padding:0"><div style="padding:0 0.25em"> <ul><li><a href="/wiki/Lunisolar_calendar" title="Lunisolar calendar">Lunisolar</a> (<a href="/wiki/Hebrew_calendar" title="Hebrew calendar">Hebrew</a>, <a href="/wiki/Hindu_calendar" title="Hindu calendar">Hindu</a>)</li> <li><a href="/wiki/Solar_calendar" title="Solar calendar">Solar</a></li> <li><a href="/wiki/Lunar_calendar" title="Lunar calendar">Lunar</a> (<a href="/wiki/Islamic_calendar" title="Islamic calendar">Islamic</a>)</li> <li><a href="/wiki/Astronomical_year_numbering" title="Astronomical year numbering">Astronomical year numbering</a></li></ul> </div></td></tr><tr><th scope="row" class="navbox-group" style="width:8.0em;font-weight:normal;background:#cc9;">Others</th><td class="navbox-list-with-group navbox-list navbox-even" style="padding:0"><div style="padding:0 0.25em"> <ul><li><a href="/wiki/Sexagenary_cycle" title="Sexagenary cycle">Chinese sexagenary cycle</a></li> <li><a href="/wiki/Geologic_Calendar" title="Geologic Calendar">Geologic Calendar</a></li> <li><a href="/wiki/Iranian_calendars" title="Iranian calendars">Iranian</a></li> <li><a class="mw-selflink selflink">ISO week date</a></li> <li><a href="/wiki/Mesoamerican_calendars" title="Mesoamerican calendars">Mesoamerican</a> <ul><li><a href="/wiki/Maya_calendar" title="Maya calendar">Maya</a></li> <li><a href="/wiki/Aztec_calendar" title="Aztec calendar">Aztec</a></li></ul></li> <li><a href="/wiki/Winter_count" title="Winter count">Winter count</a></li> <li><a href="/wiki/New_Earth_Time" title="New Earth Time">New Earth Time</a></li></ul> </div></td></tr></tbody></table><div></div></td></tr><tr><th scope="row" class="navbox-group" style="width:1%;line-height:1.2em;background:#cc9;"><a href="/wiki/Astronomical_chronology" title="Astronomical chronology">Astronomic time</a></th><td class="navbox-list-with-group navbox-list navbox-odd hlist" style="width:100%;padding:0;background:#fff;"><div style="padding:0 0.25em"> <ul><li><a href="/wiki/Cosmic_Calendar" title="Cosmic Calendar">Cosmic Calendar</a></li> <li><a href="/wiki/Ephemeris" title="Ephemeris">Ephemeris</a></li> <li><a href="/wiki/Galactic_year" title="Galactic year">Galactic year</a></li> <li><a href="/wiki/Metonic_cycle" title="Metonic cycle">Metonic cycle</a></li> <li><a href="/wiki/Milankovitch_cycles" title="Milankovitch cycles">Milankovitch cycles</a></li></ul> </div></td></tr><tr><th scope="row" class="navbox-group" style="width:1%;line-height:1.2em;background:#cc9;"><a href="/wiki/Geologic_time_scale" title="Geologic time scale">Geologic time</a></th><td class="navbox-list-with-group navbox-list navbox-odd hlist" style="width:100%;padding:0"><div style="padding:0 0.25em"></div><table class="nowraplinks navbox-subgroup" style="border-spacing:0"><tbody><tr><th scope="row" class="navbox-group" style="width:8.0em;font-weight:normal;background:#cc9;">Concepts</th><td class="navbox-list-with-group navbox-list navbox-even" style="padding:0"><div style="padding:0 0.25em"> <ul><li><a href="/wiki/Deep_time" title="Deep time">Deep time</a></li> <li><a href="/wiki/Geological_history_of_Earth" title="Geological history of Earth">Geological history of Earth</a></li> <li><a href="/wiki/Geologic_time_scale#Terminology" title="Geologic time scale">Geological time units</a></li></ul> </div></td></tr><tr><th scope="row" class="navbox-group" style="width:8.0em;font-weight:normal;background:#cc9;">Standards</th><td class="navbox-list-with-group navbox-list navbox-odd" style="padding:0"><div style="padding:0 0.25em"> <ul><li><a href="/wiki/Global_Standard_Stratigraphic_Age" title="Global Standard Stratigraphic Age">Global Standard Stratigraphic Age (GSSA)</a></li> <li><a href="/wiki/Global_Boundary_Stratotype_Section_and_Point" title="Global Boundary Stratotype Section and Point">Global Boundary Stratotype Section and Point (GSSP)</a></li></ul> </div></td></tr><tr><th scope="row" class="navbox-group" style="width:8.0em;font-weight:normal;background:#cc9;">Methods</th><td class="navbox-list-with-group navbox-list navbox-even" style="padding:0"><div style="padding:0 0.25em"> <ul><li><a href="/wiki/Chronostratigraphy" title="Chronostratigraphy">Chronostratigraphy</a></li> <li><a href="/wiki/Geochronology" title="Geochronology">Geochronology</a></li> <li><a href="/wiki/Isotope_geochemistry" title="Isotope geochemistry">Isotope geochemistry</a></li> <li><a href="/wiki/Law_of_superposition" title="Law of superposition">Law of superposition</a></li> <li><a href="/wiki/Luminescence_dating" title="Luminescence dating">Luminescence dating</a></li> <li><a href="/wiki/Samarium%E2%80%93neodymium_dating" title="Samarium–neodymium dating">Samarium–neodymium dating</a></li></ul> </div></td></tr></tbody></table><div></div></td></tr><tr><th scope="row" class="navbox-group" style="width:1%;line-height:1.2em;background:#cc9;"><a href="/wiki/Chronological_dating" title="Chronological dating">Chronological<br />dating</a></th><td class="navbox-list-with-group navbox-list navbox-odd hlist" style="width:100%;padding:0"><div style="padding:0 0.25em"></div><table class="nowraplinks navbox-subgroup" style="border-spacing:0"><tbody><tr><th scope="row" class="navbox-group" style="width:8.0em;font-weight:normal;background:#cc9;"><a href="/wiki/Absolute_dating" title="Absolute dating">Absolute dating</a></th><td class="navbox-list-with-group navbox-list navbox-odd" style="padding:0"><div style="padding:0 0.25em"> <ul><li><a href="/wiki/Amino_acid_dating" title="Amino acid dating">Amino acid racemisation</a></li> <li><a href="/wiki/Archaeomagnetic_dating" title="Archaeomagnetic dating">Archaeomagnetic dating</a></li> <li><a href="/wiki/Dendrochronology" title="Dendrochronology">Dendrochronology</a></li> <li><a href="/wiki/Ice_core" title="Ice core">Ice core</a></li> <li><a href="/wiki/Incremental_dating" title="Incremental dating">Incremental dating</a></li> <li><a href="/wiki/Lichenometry" title="Lichenometry">Lichenometry</a></li> <li><a href="/wiki/Paleomagnetism" title="Paleomagnetism">Paleomagnetism</a></li> <li><a href="/wiki/Radiometric_dating" title="Radiometric dating">Radiometric dating</a> <ul><li><a href="/wiki/Lead%E2%80%93lead_dating" title="Lead–lead dating">Lead–lead</a></li> <li><a href="/wiki/K%E2%80%93Ar_dating" title="K–Ar dating">Potassium–argon</a></li> <li><a href="/wiki/Radiocarbon_dating" title="Radiocarbon dating">Radiocarbon</a></li> <li><a href="/wiki/Uranium%E2%80%93lead_dating" title="Uranium–lead dating">Uranium–lead</a></li></ul></li> <li><a href="/wiki/Tephrochronology" title="Tephrochronology">Tephrochronology</a></li> <li><a href="/wiki/Luminescence_dating" title="Luminescence dating">Luminescence dating</a></li> <li><a href="/wiki/Thermoluminescence_dating" title="Thermoluminescence dating">Thermoluminescence dating</a></li></ul> </div></td></tr><tr><th scope="row" class="navbox-group" style="width:8.0em;font-weight:normal;background:#cc9;"><a href="/wiki/Relative_dating" title="Relative dating">Relative dating</a></th><td class="navbox-list-with-group navbox-list navbox-even" style="padding:0"><div style="padding:0 0.25em"> <ul><li><a href="/wiki/Fluorine_absorption_dating" title="Fluorine absorption dating">Fluorine absorption</a></li> <li><a href="/wiki/Nitrogen_dating" title="Nitrogen dating">Nitrogen dating</a></li> <li><a href="/wiki/Obsidian_hydration_dating" title="Obsidian hydration dating">Obsidian hydration</a></li> <li><a href="/wiki/Seriation_(archaeology)" title="Seriation (archaeology)">Seriation</a></li> <li><a href="/wiki/Stratigraphy_(archaeology)" title="Stratigraphy (archaeology)">Stratigraphy</a></li></ul> </div></td></tr></tbody></table><div></div></td></tr><tr><th scope="row" class="navbox-group" style="width:1%;line-height:1.2em;background:#cc9;">Genetic methods</th><td class="navbox-list-with-group navbox-list navbox-odd hlist" style="width:100%;padding:0"><div style="padding:0 0.25em"> <ul><li><a href="/wiki/Molecular_clock" title="Molecular clock">Molecular clock</a></li></ul> </div></td></tr><tr><th scope="row" class="navbox-group" style="width:1%;line-height:1.2em;background:#cc9;">Linguistic methods</th><td class="navbox-list-with-group navbox-list navbox-even hlist" style="width:100%;padding:0"><div style="padding:0 0.25em"> <ul><li><a href="/wiki/Glottochronology" title="Glottochronology">Glottochronology</a></li></ul> </div></td></tr><tr><th scope="row" class="navbox-group" style="width:1%;line-height:1.2em;background:#cc9;">Related topics</th><td class="navbox-list-with-group navbox-list navbox-odd hlist" style="width:100%;padding:0"><div style="padding:0 0.25em"> <ul><li><a href="/wiki/Chronicle" title="Chronicle">Chronicle</a></li> <li><a href="/wiki/New_Chronology_(Fomenko)" class="mw-redirect" title="New Chronology (Fomenko)">New Chronology</a></li> <li><a href="/wiki/Synchronoptic_view" title="Synchronoptic view">Synchronoptic view</a></li> <li><a href="/wiki/Timeline" title="Timeline">Timeline</a></li> <li><a href="/wiki/Year_zero" title="Year zero">Year zero</a></li> <li><a href="/wiki/Floruit" title="Floruit">Floruit</a></li> <li><a href="/wiki/Terminus_post_quem" title="Terminus post quem">Terminus post quem</a></li> <li><a href="/wiki/ASPRO_chronology" title="ASPRO chronology">ASPRO chronology</a></li></ul> </div></td></tr></tbody></table></div> <div class="navbox-styles"><link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1129693374"><link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1236075235"></div><div role="navigation" class="navbox" aria-labelledby="Calendars" style="padding:3px"><table class="nowraplinks mw-collapsible mw-collapsed navbox-inner" style="border-spacing:0;background:transparent;color:inherit"><tbody><tr><th scope="col" class="navbox-title" colspan="2"><link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1129693374"><link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1239400231"><div class="navbar plainlinks hlist navbar-mini"><ul><li class="nv-view"><a href="/wiki/Template:Calendars" title="Template:Calendars"><abbr title="View this template">v</abbr></a></li><li class="nv-talk"><a href="/wiki/Template_talk:Calendars" title="Template talk:Calendars"><abbr title="Discuss this template">t</abbr></a></li><li class="nv-edit"><a href="/wiki/Special:EditPage/Template:Calendars" title="Special:EditPage/Template:Calendars"><abbr title="Edit this template">e</abbr></a></li></ul></div><div id="Calendars" style="font-size:114%;margin:0 4em"><a href="/wiki/Calendar" title="Calendar">Calendars</a></div></th></tr><tr><th scope="row" class="navbox-group" style="width:1%">Systems</th><td class="navbox-list-with-group navbox-list navbox-odd hlist" style="width:100%;padding:0"><div style="padding:0 0.25em"> <ul><li><a href="/wiki/Lunar_calendar" title="Lunar calendar">Lunar</a></li> <li><a href="/wiki/Lunisolar_calendar" title="Lunisolar calendar">Lunisolar</a></li> <li><a href="/wiki/Solar_calendar" title="Solar calendar">Solar</a></li></ul> </div></td></tr><tr><th scope="row" class="navbox-group" style="width:1%">In wide use</th><td class="navbox-list-with-group navbox-list navbox-even hlist" style="width:100%;padding:0"><div style="padding:0 0.25em"> <ul><li><a href="/wiki/Astronomical_year_numbering" title="Astronomical year numbering">Astronomical</a></li> <li><a href="/wiki/Buddhist_calendar" title="Buddhist calendar">Buddhist</a></li> <li><a href="/wiki/Chinese_calendar" title="Chinese calendar">Chinese</a></li> <li><a href="/wiki/Ethiopian_calendar" title="Ethiopian calendar">Ethiopian</a></li> <li><a href="/wiki/Gregorian_calendar" title="Gregorian calendar">Gregorian</a></li> <li><a href="/wiki/Hindu_calendar" title="Hindu calendar">Hindu</a></li> <li><a href="/wiki/Islamic_calendar" title="Islamic calendar">Lunar Hijri</a></li> <li><a href="/wiki/Solar_Hijri_calendar" title="Solar Hijri calendar">Solar Hijri</a></li> <li><a class="mw-selflink selflink">ISO</a></li> <li><a href="/wiki/Unix_time" title="Unix time">Unix time</a></li></ul> </div></td></tr><tr><th scope="row" class="navbox-group" style="width:1%"><div style="display: inline-block; line-height: 1.2em; padding: .1em 0;">In more<br />limited use</div></th><td class="navbox-list-with-group navbox-list navbox-odd hlist" style="width:100%;padding:0"><div style="padding:0 0.25em"></div><table class="nowraplinks navbox-subgroup" style="border-spacing:0"><tbody><tr><td colspan="2" class="navbox-list navbox-odd" style="width:100%;padding:0"><div style="padding:0 0.25em"> <ul><li><a href="/wiki/Akan_calendar" title="Akan calendar">Akan</a></li> <li><a href="/wiki/Armenian_calendar" title="Armenian calendar">Armenian</a></li> <li><a href="/wiki/Assamese_calendar" title="Assamese calendar">Assamese (Bhāshkarābda)</a></li> <li><a href="/wiki/Assyrian_calendar" title="Assyrian calendar">Assyrian</a></li> <li><a href="/wiki/Bah%C3%A1%CA%BC%C3%AD_calendar" title="Baháʼí calendar">Baháʼí</a> <ul><li>Badí‘</li></ul></li> <li>Bali <ul><li><a href="/wiki/Pawukon_calendar" title="Pawukon calendar">Pawukon</a></li> <li><a href="/wiki/Balinese_saka_calendar" title="Balinese saka calendar">Saka</a></li></ul></li> <li><a href="/wiki/Bengali_calendars" title="Bengali calendars">Bengali</a> <ul><li><a href="/wiki/Bangladeshi_calendar" class="mw-redirect" title="Bangladeshi calendar">Bangladeshi</a></li></ul></li> <li><a href="/wiki/Berber_calendar" title="Berber calendar">Berber</a></li> <li><a href="/wiki/Borana_calendar" title="Borana calendar">Borana</a></li> <li><a href="/wiki/Burmese_calendar" title="Burmese calendar">Burmese</a></li> <li><a href="/wiki/Chinese_calendar" title="Chinese calendar">Chinese</a> <ul><li><a href="/wiki/Earthly_Branches" title="Earthly Branches">Earthly Branches</a></li> <li><a href="/wiki/Heavenly_Stems" title="Heavenly Stems">Heavenly Stems</a></li> <li><a href="/wiki/Republic_of_China_calendar" title="Republic of China calendar">Minguo</a></li> <li><a href="/wiki/Solar_term" title="Solar term">Solar term</a></li></ul></li> <li><a href="/wiki/Heathen_holidays" title="Heathen holidays">Germanic heathen</a></li> <li><a href="/wiki/Georgian_calendar" title="Georgian calendar">Georgian</a></li> <li><a href="/wiki/Hebrew_calendar" title="Hebrew calendar">Hebrew</a></li> <li><a href="/wiki/Hindu_calendar" title="Hindu calendar">Hindu</a> <ul><li><a href="/wiki/Vikram_Samvat" title="Vikram Samvat">Vikram Samvat</a></li> <li><a href="/wiki/Indian_national_calendar" title="Indian national calendar">Saka</a></li></ul></li> <li><a href="/wiki/Hmong_calendar" title="Hmong calendar">Hmong</a></li> <li><a href="/wiki/Igbo_calendar" title="Igbo calendar">Igbo</a></li> <li><a href="/wiki/Iranian_calendars" title="Iranian calendars">Iranian</a> <ul><li><a href="/wiki/Jalali_calendar" title="Jalali calendar">Jalali</a> <ul><li>medieval</li></ul></li> <li><a href="/wiki/Zoroastrian_calendar" title="Zoroastrian calendar">Zoroastrian</a></li></ul></li> <li><a href="/wiki/Irish_calendar" title="Irish calendar">Irish</a> <ul><li>Gaelic</li></ul></li> <li><a href="/wiki/Islamic_calendar" title="Islamic calendar">Islamic</a> <ul><li><a href="/wiki/Fasli_calendar" title="Fasli calendar">Fasli</a></li> <li><a href="/wiki/Tabular_Islamic_calendar" title="Tabular Islamic calendar">Tabular</a></li></ul></li> <li><a href="/wiki/Vira_Nirvana_Samvat" title="Vira Nirvana Samvat">Jain</a></li> <li><a href="/wiki/Japanese_calendar" title="Japanese calendar">Japanese</a></li> <li><a href="/wiki/Javanese_calendar" title="Javanese calendar">Javanese</a></li> <li><a href="/wiki/Korean_calendar" title="Korean calendar">Korean</a> <ul><li><a href="/wiki/Juche_calendar" title="Juche calendar">Juche</a></li></ul></li> <li><a href="/wiki/Kurdish_calendar" title="Kurdish calendar">Kurdish</a></li> <li><a href="/wiki/Lithuanian_calendar" title="Lithuanian calendar">Lithuanian</a></li> <li><a href="/wiki/Tirhuta_Panchang" title="Tirhuta Panchang">Maithili</a></li> <li><a href="/wiki/Malayalam_calendar" title="Malayalam calendar">Malayalam</a></li> <li><a href="/wiki/Mandaean_calendar" title="Mandaean calendar">Mandaean</a></li> <li><a href="/wiki/Meitei_calendar" title="Meitei calendar">Manipuri (Meitei)</a></li> <li><a href="/wiki/Melanau_calendar" title="Melanau calendar">Melanau</a></li> <li><a href="/wiki/Mongolian_calendar" title="Mongolian calendar">Mongolian</a></li> <li>Nepal <ul><li><a href="/wiki/Nepal_Sambat" title="Nepal Sambat">Nepal Sambat</a></li> <li><a href="/wiki/Vikram_Samvat" title="Vikram Samvat">Vikram Samvat</a></li> <li><a href="/wiki/Yele_Sambat" title="Yele Sambat">Yele Sambat</a></li></ul></li> <li><a href="/wiki/Nisga%27a#Nisga’a_calendar/life" title="Nisga'a">Nisg̱a'a</a></li> <li><a href="/wiki/Odia_calendar" title="Odia calendar">Odia</a></li> <li><a href="/wiki/Punjabi_calendar" title="Punjabi calendar">Punjabi</a> <ul><li><a href="/wiki/Nanakshahi_calendar" title="Nanakshahi calendar">Nanakshahi</a></li></ul></li> <li><a href="/wiki/Romanian_calendar" title="Romanian calendar">Romanian</a></li> <li><a href="/wiki/Shona_calendar" title="Shona calendar">Shona</a></li> <li><a href="/wiki/Somali_calendar" title="Somali calendar">Somali</a></li> <li><a href="/wiki/Sotho_calendar" title="Sotho calendar">Sesotho</a></li> <li><a href="/wiki/Slavic_calendar" title="Slavic calendar">Slavic</a> <ul><li><a href="/wiki/Slavic_Native_Faith%27s_calendars_and_holidays" title="Slavic Native Faith's calendars and holidays">Slavic Native Faith</a></li> <li><a href="/wiki/Macedonian_months" title="Macedonian months">Macedonian</a></li></ul></li> <li><a href="/wiki/Tamil_calendar" title="Tamil calendar">Tamil</a></li> <li><a href="/wiki/Thai_calendar" title="Thai calendar">Thai</a> <ul><li><a href="/wiki/Thai_lunar_calendar" title="Thai lunar calendar">lunar</a></li> <li><a href="/wiki/Thai_solar_calendar" title="Thai solar calendar">solar</a></li></ul></li> <li><a href="/wiki/Tibetan_calendar" title="Tibetan calendar">Tibetan</a></li> <li><a href="/wiki/Tripuri_calendar" title="Tripuri calendar">Tripuri</a></li> <li><a href="/wiki/Tulu_calendar" title="Tulu calendar">Tulu</a></li> <li><a href="/wiki/Vietnamese_calendar" title="Vietnamese calendar">Vietnamese</a></li> <li><a href="/wiki/Wheel_of_the_Year" title="Wheel of the Year">Wicca</a></li> <li><a href="/wiki/Xhosa_calendar" title="Xhosa calendar">Xhosa</a></li> <li><a href="/wiki/Yoruba_calendar" title="Yoruba calendar">Yoruba</a></li> <li><a href="/wiki/Zulu_calendar" title="Zulu calendar">Zulu</a></li></ul> </div></td></tr><tr><th scope="row" class="navbox-group" style="width:1%;font-weight:normal;">Types</th><td class="navbox-list-with-group navbox-list navbox-even" style="width:100%;padding:0"><div style="padding:0 0.25em"> <ul><li><a href="/wiki/Runic_calendar" title="Runic calendar">Runic</a></li> <li><a href="/wiki/Mesoamerican_calendars" title="Mesoamerican calendars">Mesoamerican</a> <ul><li><a href="/wiki/Mesoamerican_Long_Count_calendar" title="Mesoamerican Long Count calendar">Long Count</a></li> <li><a href="/wiki/Calendar_round" class="mw-redirect" title="Calendar round">Calendar round</a></li></ul></li></ul> </div></td></tr><tr><th scope="row" class="navbox-group" style="width:1%;font-weight:normal;">Christian variants</th><td class="navbox-list-with-group navbox-list navbox-odd" style="width:100%;padding:0"><div style="padding:0 0.25em"> <ul><li><a href="/wiki/Coptic_calendar" title="Coptic calendar">Coptic</a></li> <li><a href="/wiki/Ethiopian_calendar" title="Ethiopian calendar">Ethiopian and Eritrean</a></li> <li><a href="/wiki/Julian_calendar" title="Julian calendar">Julian</a> <ul><li><a href="/wiki/Revised_Julian_calendar" title="Revised Julian calendar">Revised</a></li></ul></li> <li><a href="/wiki/Liturgical_year" title="Liturgical year">Liturgical year</a> <ul><li><a href="/wiki/Eastern_Orthodox_liturgical_calendar" title="Eastern Orthodox liturgical calendar">Eastern Orthodox</a></li></ul></li> <li><a href="/wiki/Calendar_of_saints" title="Calendar of saints">Saints</a></li></ul> </div></td></tr></tbody></table><div></div></td></tr><tr><th scope="row" class="navbox-group" style="width:1%">Historical</th><td class="navbox-list-with-group navbox-list navbox-even hlist" style="width:100%;padding:0"><div style="padding:0 0.25em"> <ul><li><a href="/wiki/Pre-Islamic_Arabian_calendar" title="Pre-Islamic Arabian calendar">Arabian</a></li> <li><a href="/wiki/Attic_calendar" title="Attic calendar">Attic</a></li> <li><a href="/wiki/Aztec_calendar" title="Aztec calendar">Aztec</a> <ul><li><a href="/wiki/T%C5%8Dnalp%C5%8Dhualli" title="Tōnalpōhualli">Tōnalpōhualli</a></li> <li><a href="/wiki/Xiuhp%C5%8Dhualli" title="Xiuhpōhualli">Xiuhpōhualli</a></li></ul></li> <li><a href="/wiki/Babylonian_calendar" title="Babylonian calendar">Babylonian</a></li> <li><a href="/wiki/Bulgar_calendar" title="Bulgar calendar">Bulgar</a></li> <li><a href="/wiki/Byzantine_calendar" title="Byzantine calendar">Byzantine</a></li> <li><a href="/wiki/Cappadocian_calendar" title="Cappadocian calendar">Cappadocian</a></li> <li><a href="/wiki/Celtic_calendar" title="Celtic calendar">Celtic</a></li> <li><a href="/wiki/Cham_calendar" title="Cham calendar">Cham</a></li> <li><a href="/wiki/Chula_Sakarat" title="Chula Sakarat">Culāsakaraj</a></li> <li><a href="/wiki/Coligny_calendar" title="Coligny calendar">Coligny</a></li> <li><a href="/wiki/Egyptian_calendar" title="Egyptian calendar">Egyptian</a></li> <li><a href="/wiki/Enoch_calendar" title="Enoch calendar">Enoch</a></li> <li><a href="/wiki/Florentine_calendar" title="Florentine calendar">Florentine</a></li> <li><a href="/wiki/French_Republican_calendar" title="French Republican calendar">French Republican</a></li> <li><a href="/wiki/Germanic_calendar" class="mw-redirect" title="Germanic calendar">Germanic</a></li> <li><a href="/wiki/Ancient_Greek_calendars" title="Ancient Greek calendars">Greek</a></li> <li><a href="/wiki/Hindu_calendar" title="Hindu calendar">Hindu</a></li> <li><a href="/wiki/Inca_calendar" class="mw-redirect" title="Inca calendar">Inca</a></li> <li><a href="/wiki/Ancient_Macedonian_calendar" title="Ancient Macedonian calendar">Macedonian</a></li> <li><a href="/wiki/Maya_calendar" title="Maya calendar">Maya</a> <ul><li><a href="/wiki/Haab%CA%BC" title="Haabʼ">Haabʼ</a></li> <li><a href="/wiki/Tzolk%CA%BCin" title="Tzolkʼin">Tzolkʼin</a></li></ul></li> <li><a href="/wiki/Muisca_calendar" title="Muisca calendar">Muisca</a></li> <li><a href="/wiki/Pentecontad_calendar" title="Pentecontad calendar">Pentecontad</a></li> <li><a href="/wiki/Pisan_calendar" title="Pisan calendar">Pisan</a></li> <li><a href="/wiki/Qumran_calendrical_texts" title="Qumran calendrical texts">Qumran</a></li> <li><a href="/wiki/Rapa_Nui_calendar" title="Rapa Nui calendar">Rapa Nui</a></li> <li><a href="/wiki/Roman_calendar" title="Roman calendar">Roman</a></li> <li><a href="/wiki/Rumi_calendar" title="Rumi calendar"><i>Rumi</i></a></li> <li><a href="/wiki/Sexagenary_cycle" title="Sexagenary cycle">Sexagenary</a></li> <li><a href="/wiki/Soviet_calendar" title="Soviet calendar">Soviet</a></li> <li><a href="/wiki/Swedish_calendar" title="Swedish calendar">Swedish</a></li> <li><a href="/wiki/2002_renaming_of_Turkmen_months_and_days_of_week" title="2002 renaming of Turkmen months and days of week">Turkmen</a></li></ul> </div></td></tr><tr><th scope="row" class="navbox-group" style="width:1%">By specialty</th><td class="navbox-list-with-group navbox-list navbox-odd hlist" style="width:100%;padding:0"><div style="padding:0 0.25em"> <ul><li><a href="/wiki/Holocene_calendar" title="Holocene calendar">Holocene</a> <ul><li>anthropological</li></ul></li> <li><a href="/wiki/Proleptic_Gregorian_calendar" title="Proleptic Gregorian calendar">Proleptic Gregorian</a> / <a href="/wiki/Proleptic_Julian_calendar" title="Proleptic Julian calendar">Proleptic Julian</a> <ul><li>historiographical</li></ul></li> <li><a href="/wiki/Darian_calendar" title="Darian calendar">Darian</a> <ul><li>Martian</li></ul></li> <li><a href="/wiki/Dreamspell" title="Dreamspell">Dreamspell</a> <ul><li>New Age</li></ul></li> <li><a href="/wiki/Discordian_calendar" title="Discordian calendar">Discordian</a></li> <li><a href="/wiki/%27Pataphysics#Pataphysical_calendar" title="'Pataphysics">'Pataphysical</a></li></ul> </div></td></tr><tr><th scope="row" class="navbox-group" style="width:1%"><a href="/wiki/Calendar_reform" title="Calendar reform">Reform proposals</a></th><td class="navbox-list-with-group navbox-list navbox-even hlist" style="width:100%;padding:0"><div style="padding:0 0.25em"> <ul><li><a href="/wiki/Hanke%E2%80%93Henry_Permanent_Calendar" title="Hanke–Henry Permanent Calendar">Hanke–Henry Permanent</a></li> <li><a href="/wiki/International_Fixed_Calendar" title="International Fixed Calendar">International Fixed</a></li> <li><a href="/wiki/Pax_Calendar" title="Pax Calendar">Pax</a></li> <li><a href="/wiki/Positivist_calendar" title="Positivist calendar">Positivist</a></li> <li><a href="/wiki/Symmetry454" title="Symmetry454">Symmetry454</a></li> <li><a href="/wiki/World_Calendar" title="World Calendar">World</a></li></ul> </div></td></tr><tr><th scope="row" class="navbox-group" style="width:1%"><div style="display: inline-block; line-height: 1.2em; padding: .1em 0;">Displays and<br />applications</div></th><td class="navbox-list-with-group navbox-list navbox-odd hlist" style="width:100%;padding:0"><div style="padding:0 0.25em"> <ul><li><a href="/wiki/Calendaring_software" class="mw-redirect" title="Calendaring software">Electronic</a></li> <li><a href="/wiki/Perpetual_calendar" title="Perpetual calendar">Perpetual</a></li> <li><a href="/wiki/Calendar_(stationery)" title="Calendar (stationery)">Wall</a></li></ul> </div></td></tr><tr><th scope="row" class="navbox-group" style="width:1%"><div style="display: inline-block; line-height: 1.2em; padding: .1em 0;">Year naming<br />and numbering</div></th><td class="navbox-list-with-group navbox-list navbox-odd hlist" style="width:100%;padding:0"><div style="padding:0 0.25em"></div><table class="nowraplinks navbox-subgroup" style="border-spacing:0"><tbody><tr><th scope="row" class="navbox-group" style="width:1%;font-weight:normal;">Terminology</th><td class="navbox-list-with-group navbox-list navbox-even" style="width:100%;padding:0"><div style="padding:0 0.25em"> <ul><li><a href="/wiki/Calendar_era" title="Calendar era">Era</a></li> <li><a href="/wiki/Epoch" title="Epoch">Epoch</a></li> <li><a href="/wiki/Leap_year" title="Leap year">Leap year</a></li> <li><a href="/wiki/New_Year" title="New Year">New Year</a></li> <li><a href="/wiki/Regnal_name" title="Regnal name">Regnal name</a></li> <li><a href="/wiki/Regnal_year" title="Regnal year">Regnal year</a></li> <li><a href="/wiki/Year_zero" title="Year zero">Year zero</a></li></ul> </div></td></tr><tr><th scope="row" class="navbox-group" style="width:1%;font-weight:normal;">Systems</th><td class="navbox-list-with-group navbox-list navbox-odd" style="width:100%;padding:0"><div style="padding:0 0.25em"> <ul><li><a href="/wiki/Ab_urbe_condita" title="Ab urbe condita">Ab urbe condita</a></li> <li><a href="/wiki/Anka_year" title="Anka year">Anka year</a></li> <li><a href="/wiki/Anno_Domini" title="Anno Domini">Anno Domini</a>/<a href="/wiki/Common_Era" title="Common Era">Common Era</a></li> <li><a href="/wiki/Anno_Lucis" title="Anno Lucis">Anno Lucis</a></li> <li><a href="/wiki/Era_of_the_Martyrs" title="Era of the Martyrs">Anno Martyrum</a></li> <li><a href="/wiki/Anno_Mundi" title="Anno Mundi">Anno Mundi</a></li> <li><a href="/wiki/Eponym_dating_system" title="Eponym dating system">Assyrian</a></li> <li><a href="/wiki/Before_Present" title="Before Present">Before Present</a></li> <li><a href="/wiki/Chinese_era_name" title="Chinese era name">Chinese Imperial</a></li> <li><a href="/wiki/Republic_of_China_calendar" title="Republic of China calendar">Chinese Minguo</a></li> <li><a href="/wiki/Regnal_years_of_English_and_British_monarchs" title="Regnal years of English and British monarchs">English and British regnal year</a></li> <li><a href="/wiki/Hijri_year" title="Hijri year">Hijri year</a></li> <li><a href="/wiki/Holocene_calendar" title="Holocene calendar">Human (Holocene)</a></li> <li><a href="/wiki/Japanese_era_name" title="Japanese era name">Japanese</a></li> <li><a href="/wiki/Korean_era_name" title="Korean era name">Korean</a></li> <li><a href="/wiki/Nirayana_system" title="Nirayana system">Nirayana system</a></li> <li><a href="/wiki/Seleucid_era" title="Seleucid era">Seleucid</a></li> <li><a href="/wiki/Spanish_era" title="Spanish era">Spanish</a></li> <li><a href="/wiki/Yuga" title="Yuga">Yugas</a> <ul><li><a href="/wiki/Satya_Yuga" title="Satya Yuga">Satya</a></li> <li><a href="/wiki/Treta_Yuga" title="Treta Yuga">Treta</a></li> <li><a href="/wiki/Dvapara_Yuga" title="Dvapara Yuga">Dvapara</a></li> <li><a href="/wiki/Kali_Yuga" title="Kali Yuga">Kali</a></li></ul></li> <li><a href="/wiki/Vietnamese_era_name" title="Vietnamese era name">Vietnamese</a></li></ul> </div></td></tr></tbody></table><div></div></td></tr><tr><th scope="row" class="navbox-group" style="width:1%">Fictional</th><td 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