The history of Leap Day

Today is Leap Day, a once-every-four-year event when February 29 is added to calendars worldwide. But have you ever wondered why an extra day is added in February instead of, say, December? Or why Leap Days even exist at all?

Let’s start at the beginning: Roman Emperor Julius Caesar first introduced Leap Day in 46 BCE as part of his Julian calendar, which counted each year at 365.25 days. It added an extra day once every four years to account for the fact that Earth’s full orbit around the Sun isn’t precisely 365 days, but about six hours longer than that.

The Julian calendar scheduled that extra day for late February, since many ancient cultures believed the world was created in the spring, and March was the beginning of the year – thus, Leap Day was placed at year’s end.

• Over the following centuries, the Western world used the Julian calendar as a template until Pope Gregory XIII introduced the Gregorian calendar in the late 1500s.
• This method of timekeeping, which is still used today, chose to keep Leap Days at the end of February for continuity.

📅 Fun fact: If Leap Day didn’t exist, summer and winter would fully swap places on the calendar – aka hot girl winters and cold girl summers – over the next ~750 years.