Why Are There Only 28 Days in February?

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They write new content and verify and edit content received from contributors.</div> </a> <div data-popper-arrow></div> </div> <span class="btn btn-link editor-link p-0 qa-byline-link font-12 "> The Editors of Encyclopaedia Britannica</span></div></div> </div> <article class="topic-content content mt-20"><figure class="md-assembly md-feature-assembly print-false" data-type="1" data-descid="1"><div class="md-assembly-wrapper card-media" data-type="image"><a href="https://cdn.britannica.com/17/191117-050-189A80C0/Calendar.jpg" target="_blank" class="gtm-assembly-link position-relative d-flex align-items-center justify-content-center " data-href="*"><img src="https://cdn.britannica.com/17/191117-050-189A80C0/Calendar.jpg?w=600&q=60" alt="Calendar showing the month of February" data-width="1600" data-height="1067" loading="eager"><button class="magnifying-glass btn btn-circle position-absolute shadow btn-white top-10 right-10" aria-label="Zoom in"><em class="material-icons link-blue" data-icon="zoom_in"></em></button></a></div><figcaption class=""><div class="md-assembly-caption text-muted font-14 font-serif line-clamp"><span><button class="js-more-btn d-none btn btn-unstyled font-12 bg-white js-content" aria-label="Toggle more/less fact data"><span class="link-blue">(more)</span></button></span></div><cite class="credit d-block mt-5">© Tanusha/Fotolia</cite></figcaption></figure><p class="topic-paragraph">Each month in the modern <a href="https://www.britannica.com/topic/Gregorian-calendar" class="md-crosslink " data-show-preview="true">Gregorian calendar</a> consists of at least 28 days. That number would be a nicely rounded 30 were it not for <a href="https://www.britannica.com/topic/February" class="md-crosslink " data-show-preview="true">February</a>. While every month besides the second in the calendar contains at least 30 days, February falls short with 28 (and 29 on a leap year). So why is the most widely used calendar in the world so inconsistent in the lengths of its months? And why is February stuck with the fewest number of days? Blame it on Roman superstition.<figure class="md-assembly md-feature-assembly print-false" data-type="3" data-descid="7"><div class="md-assembly-wrapper card-media" data-type="video" video-id="253592"><a data-id="253592" class="gtm-assembly-link d-flex justify-content-center" style="--aspect-ratio: 16/9" href="/video/What-is-Leap-Day-Gregorian-calendar-29-days-in-February/-298178"><img src="https://cdn.britannica.com/92/253592-138-8FD23B6E/What-is-Leap-Day-Gregorian-calendar-29-days-in-February.jpg?w=800&h=450&c=crop" alt="What is Leap Day? Explanation of a leap year, a year in the Gregorian calendar when February has 29 days instead of 28." loading="lazy"><script type="application/json"> { "sources": [ { "file" : "//content.jwplatform.com/manifests/Ia094xZV.m3u8" } ], "image": "https://cdn.britannica.com/92/253592-138-8FD23B6E/What-is-Leap-Day-Gregorian-calendar-29-days-in-February.jpg" ,"tracks": [ { "file" : "//assets-jpcust.jwpsrv.com/tracks/93NlaX3o.vtt", "label": "English" } ] ,"adfile": "//content.jwplatform.com/manifests/i7eFrRs3.m3u8" } </script><div class="btn btn-xl btn-white btn-circle position-absolute shadow" style="top: 50%; transform: translateY(-50%)"><em class="material-icons" data-icon="play_arrow"></em></div></a></div><figcaption class=""><div class="md-assembly-caption text-muted font-14 font-serif line-clamp"><span><span class="md-assembly-title font-weight-bold mr-5 d-inline font-sans-serif md-video-caption" video-control="253592">What is Leap Day?</span><span>An extra day is added to the calendar about every four years. Why?</span><button class="js-more-btn d-none btn btn-unstyled font-12 bg-white js-content" aria-label="Toggle more/less fact data"><span class="link-blue">(more)</span></button></span></div><cite class="credit d-block mt-5">Encyclopædia Britannica, Inc.</cite></figcaption></figure></p><span class="MOD1"></span><p class="topic-paragraph">The Gregorian calendar’s oldest ancestor, the first Roman calendar, had a glaring difference in structure from its later variants: it consisted of 10 months rather than 12. <strong>In order to fully sync the calendar with the lunar year, the Roman king <a href="https://www.britannica.com/biography/Numa-Pompilius" class="md-crosslink " data-show-preview="true">Numa Pompilius</a> added January and February to the original 10 months.</strong> The previous calendar had had 6 months of 30 days and 4 months of 31, for a total of 304 days. However, Numa wanted to avoid having even numbers in his calendar, as Roman superstition at the time held that even numbers were unlucky. He subtracted a day from each of the 30-day months to make them 29. The lunar year consists of 355 days (354.367 to be exact, but calling it 354 would have made the whole year unlucky!), which meant that he now had 56 days left to work with. In the end, at least 1 month out of the 12 needed to contain an even number of days. This is because of simple mathematical fact: the sum of any even amount (12 months) of odd numbers will always equal an even number—and he wanted the total to be odd. <strong>So Numa chose February, a month that would be host to Roman rituals honoring the dead, as the unlucky month to consist of 28 days.</strong></p><span class="MOD2"></span><p class="topic-paragraph">Despite changes in the calendar as it was altered after Numa’s additions—alterations that include the shortening of February at certain intervals, the addition of a leap month, and eventually the modern leap day—February’s 28-day length has stuck.</p><span class="MOD3"></span><span class="AM-END-OF-ARTICLE am-inline"></span></article> </div> </div> </div> <aside class="cm-rightrail d-none d-md-block ad-rail"></aside> </div> </div> </div> </div> </main> <div class="grid gx-0"> <div class="col"> <div class="md-loading hidden display-4 font-weight-normal"></div> <div class="text-center my-20 mb-100"> <button class="md-infinite-load-next btn btn-blue" data-value="next-page">Load More</button> </div> </div> <div class="col-md-da-320 hidden-xs"> </div> </div> </div> </div> </main> <div id="md-footer"></div> <noscript><iframe src="//www.googletagmanager.com/ns.html?id=GTM-5W6NC8" height="0" width="0" style="display:none;visibility:hidden"></iframe></noscript>  <script> window.ap3c = window.ap3c || {}; var ap3c = window.ap3c; ap3c.cmd = ap3c.cmd || []; ap3c.cmd.push(function() { ap3c.init('ZO4siT4cLwnykPnzZWJtd3Byb2Q', 'https://engage.email.britannica.com/'); ap3c.track({v: 0}); }); ap3c.activity = function(act) { ap3c.act = (ap3c.act || []); ap3c.act.push(act); }; var s, t; s = document.createElement('script'); s.type = 'text/javascript'; s.src = "https://engage.email.britannica.com/app.js"; t = document.getElementsByTagName('script')[0]; t.parentNode.insertBefore(s, t); </script> <script class="marketing-page-info" type="application/json"> {"pageType":"Story","templateName":"DEMYSTIFIED","pageNumber":1,"pagesTotal":10,"pageId":5846,"pageLength":null,"initialLoad":true,"lastPageOfScroll":false} </script> <script class="marketing-content-info" type="application/json"> [] </script> <script src="https://cdn.britannica.com/mendel-resources/3-133/js/libs/jquery-3.5.0.min.js?v=3.133.36"></script> <script type="text/javascript" data-type="Init Mendel Code Splitting"> (function() { $.ajax({ dataType: 'script', cache: true, url: 'https://cdn.britannica.com/mendel-resources/3-133/dist/story-page.js?v=3.133.36' }); })(); </script> <script class="analytics-metadata" type="application/json"> {"leg":"B","adLeg":"B","userType":"ANONYMOUS","pageType":"Story","pageSubtype":"DEMYSTIFIED","articleTemplateType":null,"gisted":false,"pageNumber":1,"hasSummarizeButton":false,"hasAskButton":false} </script> <script type="text/javascript"> EBStat={accountId:-1,hostnameOverride:'webstats.eb.com',domain:'www.britannica.com', json:''}; </script> <script type="text/javascript"> ( function() { $.ajax( { dataType: 'script', cache: true, url: '//www.britannica.com/webstats/mendelstats.js?v=1' } ) .done( function() { try {writeStat(null,EBStat);} catch(err){} } ); })(); </script> <div id="bc-fixed-dialogue"></div> </body> </html>

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Why Are There Only 28 Days in February? | Britannica