For many, the obscure existence of February 30th may seem shocking. However, the world of calendars saw many adjustments in the modern era when the European Renaissance took shape. Within that time, Sweden had to invent this date to fix its miscalculations when transitioning from the Julian calendar to the Gregorian one.
A brief history of calendars
Measurements have been used by different means in various cultures, but the modern calendar we use today originates from the Julian calendar. Emperor Julius Caesar recognised the importance of a unified measurement and implemented a strict system of 365 days a year.
On a different note, the leap days arose because the earth does not take a complete 365 days, but rather a little over 365.2422, to be more precise. The Julian calendar rounded this to 365.25; that extra day was counted every 4 years as the 29th day in February.
The problem arose when this slight overestimate accumulated over the years, and the church witnessed a problem with celebrating Easter because the accumulated time had summed up to an 11-day excess, which meant Easter this time around would miss the alignment with the spring equinox.
To solve this excess 11-day problem, Pope Gregory XIII ordered a reform, skipping 10 days (October 4th, 1582, followed by October 15th, 1582) and adjusting leap year rules to prevent future drift. This is the modern calendar, now known as the Gregorian calendar.
The need for February 30th
The European nations all adhered to the Pope’s wishes and adjusted their calendars to resemble the Gregorian one, yet Sweden found this troublesome.
The plan initially was to skip leap years from 1700 to 1740 to gradually align with the Gregorian calendar. However, the Swedes in this completed mission forgot to record the leap year for two separate years, 1704 and 1708, which meant they were entirely out of sync with the Gregorian calendar and the old Julian one.
Sweden decided to revert to the Julian calendar by adding an extra leap day in 1712, which resulted in February having 30 days instead of 28 or 29. This reversal kept Sweden stuck in the Julian calendar for several decades while Europe moved on. By 1753, the date discrepancy again had grown to 11 days, just like the Pope had observed when he first decided to skip them to align with Easter, as most of Europe had already switched to the Gregorian system. To finally align with the Gregorian calendar, Sweden skipped 11 days—going directly from February 17th, 1753, to March 1st, 1753. This officially aligned Sweden with most of Western Europe’s calendar system.
This anomaly is widely recognised as the mistakenly occurring February 30th, which proves that humans had a long adjustment period filled with calculations, scientific influences, and political influences that culminated in the world of the shared Gregorian calendar we take for granted today.