In case you haven’t been paying attention, we have an extra day in the calendar this year. That’s right: February 29 is happening, because 2024 is a leap year, and rather than having 365 days, we’ll have 366 this year.

Why We Have Leap Years: A Refresher

Most of us learned the reason for leap day way back in elementary school, so here’s a quick refresher: It takes 365.2422 days for our planet to complete one revolution around the sun. That translates into the problematic conclusion that every 365-day year ends six hours short of a complete orbit. Instead of trying to figure out some bizarre way to add a quarter of a day into each year (can you imagine), we simply add one whole day every four years to make up for the discrepancy. Well … mostly.

We don’t actually have leap years every four years. There are a few exceptions to the rule, thanks to the fact that the sun takes 365.2422 days — not a tidy 365.25 — to complete its path (and this, ladies and gentlemen, is why being specific matters). Those tiny decimals might not seem important, but over hundreds of years they’d be enough to throw our whole system off. That’s why this dizzying rule exists: 

Leap years divisible by 100, like the year 1900, are skipped unless they’re also divisible by 400, like the year 2000, in which case they’re observed. 

Dropping those three leap days every 400 years keeps our calendar on time.

Who Came Up With This System?

The concept of a leap year was really the result of a group effort. Many ancient calendars — including the Hebrew, Chinese and Buddhist calendars — were lunisolar, meaning their dates took the position of the moon as well as the position of the Earth relative to the sun into account. Since that creates a gap of about 11 days, those calendars all had periodic “extra” months, known as intercalary or interstitial months, to keep the year on track. 

Our calendar as we know it is a tweaked version of what the ancient Romans used to keep time. According to, historians still aren’t quite sure how the early Romans’ system worked, though, mainly because even the early Romans didn’t know what they were doing. Nonetheless, they had an intercalary month known as Mercedonius to account for the difference between their year and the solar year, and they would often insert it somewhere into the month of February. When Mercedonius occurred would be up to the consuls to decide, which apparently irked Julius Caesar when he came to power. So Caesar (who admired the Egyptians’ 365-day solar calendar) and the philosopher Sosigenes of Alexandria came up with the calendar we know today. The Julian calendar, as it is commonly known, took effect on January 1, 45 B.C.E. It consisted of 365 days, and one extra day in February (to keep with the Roman tradition of messing with that month in particular) every four years.

“But what about the exceptions rule?” you ask. That was devised by the Catholic Church, which noticed by the 16th century that Easter had drifted away from its traditional place (the first Sunday after the first full moon following the vernal equinox, to be specific). Pope Gregory XIII commissioned the modified calendar to account for the discrepancy, and thus the Gregorian calendar was born.

Fun Facts About Leap Year

  • People who are born on February 29 are called “leaplings,” and there are only about 5 million leaplings in the whole world.
  • In 5th-century Ireland, St. Bridget lamented to St. Patrick that women were not allowed to propose marriage to men. So, legend has it that St. Patrick designated February 29 as Bachelor’s Day, a kind of Opposite Day when women would be allowed to propose to men.
  • The term “leap year” comes from the fact that from March onward, each date of a leap year moves forward — or leaps — an extra day from the previous year. So for example, March 1, 2023, was a Wednesday, and if this weren’t a leap year the same date would be a Thursday in 2024. But instead, it will fall on a Friday.
  • Momentous events that occurred during leap years: 
    • Rome burned (64)
    • Titanic sank (1912)
    • Pilgrims landed at Plymouth, Massachusetts (1620)
    • Benjamin Franklin proved that lightning is electricity (1752)
    • Gold was discovered in California (1848)

Image by sofyabolotinaphotos, via

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