Why Do We Have Leap Years? Everything to Know

2024 is a Leap Year, a year that comes every 4 years in which there are 366 days rather than 365 days. Read on to learn more about what leap years are, why we have them, the history behind their celebration, and other interesting facts, including what to do when your birthday lands on February 29th.

What is a Leap Year and Why Do We Have it?‍

The Earth doesn’t spin around the sun in exactly 365 days. It actually takes an extra 5 hours, 48 minutes, and 45 seconds longer than that, making the solar year 365.242 days. This means that, if we don’t account for that extra time, our calendar will fall behind the seasons we’re used to. So, in 750 years, June would start in the middle of winter. Throughout history, we’ve tried to account for this in different ways. Today, we remedy this by, every 4 years, adding an extra day to the end of February – the 29th.

But even that doesn’t completely solve the problem. So we have to add in a few little extra rules you’ll see explained below.

We all know that leap years are the years that are divisible by 4 (i.e. 2012, 2016, 2020, 2024, etc.), but there are some exceptions to this rule, which can get kind of confusing. To put it as simply as possible, if the year is also divisible by 100 (i.e. 1800, 1900, etc.), it is NOT a leap year. However, if it is divisible by 100, but also divisible by 400 (i.e. 1600, 2000, etc.), then it actually is a leap year. If that was confusing. see our handy chart above to help you easily determine when it’s a leap year!

History of Leap Years

‍Throughout history, humans have dealt with the fact that the solar year doesn’t line up with our calendar in many different ways. The ancient Sumerian calendar of 5,000 years ago very simply divided the year into 12 months with 30 days each. With just 360 days, this calendar was an entire week shorter than the Earth’s orbit around the sun. The Egyptians who adopted this calendar attempted to solve that problem by adding an extra 5 days of festivals and partying at the end of the year.

The Egyptians eventually began observing a 365-day year with a leap-year system. But the Romans were still behind, trying to adjust their calendar by randomly adding days or months here and there. In 46 BC, Julius Caesar declared they would, for just one year, take on a 445-day calendar he called the Year of Confusion. The idea behind this decree was to all at once correct the damage that had already been done from years of drifting out of sync with the seasons. After this, he ordered a 365.25-day year with a leap day added every four years.

But even this change wasn’t good enough. Since 365.25 days, while close, is still longer than the 365.2422-day solar year, Pope Gregory XIII eventually created the Gregorian calendar that we currently follow in which a leap day is occasionally skipped. This makes the average year 365.2425 days long – much closer to the solar 365.2422-day year. While this still doesn’t perfectly line up with the solar year, it will be 3,300 years before this calendar begins to diverge from our solar year by a day.

What Happens if Your Birthday is on a Leap Day?

If you were born on February 29th, you might be called a “leapster” or a “leapling.” About 5 million people on earth were born on February 29th. Out of 7.5 billion people, that means 0.07% of people on earth are leapsters.

So which day do you celebrate your birthday on when it’s not a leap year? Among leapsters, it seems to be split almost 50/50. Many who celebrate on February 28th – “28thers” – are avid “February babies” who identify with being born in the month of February and refuse to be “March babies.” Those who celebrate on March 1 – “1sters” – hold tight to the idea that they were born on the day after February 28th, which is March 1st on non-leap years. Other leaplings choose to celebrate the moment the clock hits midnight between the 28th and the 1st. Others still, choose to celebrate on both days! After all, why choose sides when you could double the party?

Fun Facts About Leap Day

1. The chances of having a birthday on February 29th are about one in 1,461.

2. When adding an extra day doesn’t cut it, we’ve had to do things like adding a “leap second.” This last happened on June 30, 2015.

3. The Titanic sunk on a leap year (1912).

4. The official animal of leap day is the Australian rocket frog who can leap over 50 times his own body length.

Enjoy Your Leap Day!

‍Now that you know more about leap years, make sure to celebrate this unusual time. This unique day comes just once every 4 years, so make the most of it!

And happy birthday to all the leaplings out there! Enjoy your special day.

Sources: History.com, National Geographic, Vox