Leap Year Checker & Explainer
Check if any year is a leap year, and see exactly why — plus the nearest leap years before and after it.
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About this tool
A leap year adds an extra day (29 February) to keep the calendar lined up with Earth's orbit around the Sun. The Gregorian calendar rule is: a year is a leap year if it is divisible by 4 — except century years, which must also be divisible by 400. That's why 2000 was a leap year, but 1900 and 2100 are not: they're divisible by 4 but not by 400, so the century exception removes the extra day in those cases.
- Why isn't every year divisible by 4 a leap year?
- A 365.25-day average (the "divisible by 4" rule alone) is very slightly too long. Removing 3 leap days every 400 years (the century exception, with 400 itself kept as an exception to the exception) brings the average much closer to the real length of a solar year.