Leap Year Checker
Check any year, and see exactly which rule made it a leap year (or not).
Last updated
Enter a year above.
—Days in February
—Previous leap year
—Next leap year
The rule
A year is a leap year if it's divisible by 4 — unless it's also divisible by 100, in which case it isn't — unless it's also divisible by 400, in which case it is after all. That last exception is why 2000 was a leap year but 1900 and 2100 are not: this three-tier rule keeps the Gregorian calendar's average year length within about 26 seconds of the actual solar year.
Nothing entered here is sent to a server — the entire calculation runs as JavaScript in your browser tab.