Why are there leap years, and how do they keep calendars accurate?

There are leap years because Earth takes a little more than 365 days to go around the Sun, and we need calendars to match that.

Imagine you have a toy car that goes around a track. If it took exactly 365 laps to complete one full circle, you could just count each day like counting each lap. But if it took 365-and-a-bit laps, sometimes you'd be ahead of where you should be, like when the toy car is going faster than expected.

That extra bit is about 0.25 days, which means every year, we get a little out of sync with the seasons. After four years, that adds up to one full day, so we add an extra day in February: February 29!

Think of your favorite sandwich. If you always eat it on Monday, but sometimes you skip a week, your sandwich might come on a different day. That’s like what happens with the seasons if we don’t have leap years, spring might start on a Tuesday instead of a Monday.

By adding that extra day every four years, our calendar stays in step with Earth's journey around the Sun, keeping everything in sync!