Leap Year Calculator

Check whether any year is a leap year, and see the rule that decides it.

The leap year rule

A year is a leap year if it is divisible by 4, except century years, which must also be divisible by 400. So 2024 is a leap year, but 2100 is not, even though 2100 is divisible by 4.

The rule exists because a real year is not exactly 365 days, it is close to 365.2422. Adding a day every 4 years overcorrects slightly, so 3 of every 400 century years skip the extra day to bring the calendar back in line with the actual solar year.

Worked examples

2000: divisible by 4 and by 400, so it is a leap year despite being a century year.

1900: divisible by 4 and by 100, but not by 400, so the century exception applies and it is not a leap year.

2024: divisible by 4, not a century year, so it is a leap year, with 29 days in February.

Common questions

Yes. 2024 is divisible by 4 and is not a century year, so it has 366 days and a February 29.
No. 2025 is not divisible by 4, so it has 365 days.
Both are divisible by 4 and by 100, which normally rules a century year out. The extra exception is that a century year divisible by 400 stays a leap year, and 2000 divided by 400 is exact while 1900 is not.
Roughly once every 4 years, or exactly 97 times in every 400 years once the century exception is applied.
Their birthday only exists on the calendar in a leap year. Most legal systems treat February 28 as their birthday in the other three years; a few use March 1 instead. See the Age Calculator for how this site's own date arithmetic handles it.

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