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Leap Year Checker
Check whether any year is a leap year, and see exactly why.
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Reason
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About this tool
Enter any year to instantly find out whether it's a leap year, along with the exact rule that decides it — February gets a 29th day in leap years.
Frequently asked questions
- What's the actual rule for leap years?
- A year is a leap year if it's divisible by 4 — except century years (divisible by 100), which are only leap years if also divisible by 400. That's why 2000 was a leap year but 1900 was not.
- Why does this rule exist?
- A solar year is about 365.2422 days, not exactly 365. Adding a leap day roughly every 4 years keeps the calendar aligned with the seasons, and the century exception fine-tunes it further since 365.25 slightly overcorrects.
- Does this work for years before year 1?
- The calculation supports negative (BCE) years mathematically, though the Gregorian calendar itself wasn't in use that far back historically.