Leap Year Checker
Type any year to find out if it is a leap year, then see the next leap years coming up.
Runs entirely in your browser. No year you type is ever uploaded.
How to use this tool
Type a year into the box and press Check year. The leap year checker instantly answers the question "is it a leap year" and shows you why. You can also press Use this year to test the current year, or read the table of upcoming leap years that appears below your result. There is nothing to install and nothing to sign up for.
The leap year rules
- it is divisible by 4, AND
- it is NOT divisible by 100, UNLESS it is also divisible by 400.
In short: divisible by 4 = yes, divisible by 100 = no, divisible by 400 = yes again.
These three leap year rules exist because a year is not exactly 365 days long. Earth takes about 365.2422 days to orbit the Sun. Adding one extra day every four years gets us close, but it slightly overcorrects, so we skip the leap day on years divisible by 100. That skip overcorrects again, so we put the leap day back on years divisible by 400. Following all three steps keeps the calendar lined up with the seasons over the long run.
A real example
Take the year 1900. It is divisible by 4, which would normally make it a leap year. But it is also divisible by 100, and it is not divisible by 400, so the rules say 1900 was a common year with only 365 days. Now take 2000. It is divisible by 4 and by 100, but because it is also divisible by 400, it stays a leap year with 366 days. The year 2024 is the simple case: divisible by 4 and not by 100, so it is a leap year too.
Common questions
How does the leap year checker decide the answer?
It applies the same leap year rules a calendar uses: the year must be divisible by 4, must not be divisible by 100, unless it is also divisible by 400. If those conditions pass, the year has 366 days and a February 29.
Is it a leap year if the year is divisible by 100?
Usually not. A year divisible by 100 is a common year unless it is also divisible by 400. So 1700, 1800, and 1900 were not leap years, but 1600 and 2000 were.
Why is February 29 the extra day?
February has always been the shortest month in the modern calendar, so the extra day needed to balance the year is added to the end of it. In a leap year February has 29 days instead of 28.
Can I validate a leap year far in the past or future?
Yes. The tool can validate a leap year for any whole number you enter, including ancient and far-future years. Keep in mind the modern (Gregorian) rules were adopted at different times in different places, so very old dates may differ from historical calendars.
What years are the next leap years?
After you check a year, the table lists the upcoming leap years starting from that point. Leap years normally come every four years, with the rare skip on century years that are not divisible by 400.