Leap Year Checker
Gregorian calendar rules explained
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Result
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Days in February
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Previous leap year
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Next leap year
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Rule applied
The 3-step rule
A year is a leap year if (1) divisible by 4, AND (2) NOT divisible by 100, OR (3) divisible by 400. So 1900 was NOT a leap year but 2000 was.
Related tools
Why do leap years exist?
Earth's year is ~365.2422 days, not exactly 365. Adding a leap day every 4 years keeps the calendar aligned with the seasons. Without adjustment, July would drift into winter within a few hundred years.
- Divisible by 4 → leap year (e.g., 2024)
- Divisible by 100 but NOT 400 → NOT a leap year (e.g., 1900, 2100)
- Divisible by 400 → leap year (e.g., 2000, 2400)
Common gotcha: people assume every 4 years is leap. The century rule (100 but not 400) makes 1900, 2100, 2200 NOT leap years even though they're divisible by 4.