How to know if a year is a leap year

A leap year has 366 days instead of 365, thanks to an extra February 29. It happens almost every 4 years — but there are important exceptions.

The rule in 3 steps

1. Divisible by 4? If not, not a leap year. (Done.)
2. Divisible by 100? If not, it is a leap year. If yes, go to step 3.
3. Divisible by 400? If yes, it is; if not, it isn't.

In short: divisible by 4, except centuries not divisible by 400.

2000 vs 1900

Both are divisible by 100. But only 2000 is divisible by 400 — so 2000 was a leap year and 1900 wasn't. The next "leap century" is 2400.

Quick examples

• 2024 → divisible by 4, not 100 → leap
• 2025 → not divisible by 4 → no
• 2100 → divisible by 100, not 400 → not leap

Why it exists

Earth takes ~365.2422 days to orbit the Sun, not exactly 365. Without correction, the calendar would drift from the seasons. The extra day every 4 years fixes most of it; the century exceptions handle the small remainder.

FAQ

When do Feb 29 babies celebrate? In non-leap years, usually Feb 28 or Mar 1.