How Does Leap Years Don't Happen Every 4 Years Work?

Leap years don’t happen every 4 years because Earth takes a little more than 365 days to go around the Sun.

Imagine you're playing a game where you count how many times you go around a tree in your backyard. If it took you exactly 365 steps each time, you'd add one step (or day) every year. But if it actually takes you 365 and a quarter steps, then after four years, you’d have taken an extra full step, that’s when we get a leap year!

Earth goes around the Sun in about 365.25 days. That's like having 365 days and a little bit more, like one-quarter of a day.

• If we didn’t add an extra day every few years, our calendar would slowly get out of sync with the seasons.
• So we add a special day, February 29, to keep things in line!

Most years are leap years if they're divisible by 4. But there's a catch:

If the year is also divisible by 100, it’s not a leap year.

But wait! If it's also divisible by 400, then it is a leap year.

So 2000 was a leap year, but 1900 wasn't, just like your favorite toy works only some of the time!