Leap Year Checker
A leap year is a year with 366 days instead of the usual 365, with the extra day added as February 29. The Gregorian calendar rule is: a year is a leap year if it is divisible by 4, except for century years (divisible by 100), which must also be divisible by 400. For example, 2000 and 2400 are leap years, but 1900 and 2100 are not.
Leap years exist to keep the calendar in alignment with Earth's orbit around the Sun, which takes approximately 365.2422 days. Without periodic corrections, the calendar would drift by about 24 days over 100 years, causing seasonal dates to shift significantly. This checker instantly tells you whether any year is a leap year and shows nearby leap years for quick reference.
How it works
A year Y is a leap year if: (Y % 4 === 0 AND Y % 100 !== 0) OR (Y % 400 === 0). Century years must pass the extra divisibility-by-400 test.
Use cases
- Determining whether February 29 exists in a given year
- Planning software date logic that handles leap-year edge cases
- Calculating exact durations between dates across leap years
- Trivia and history research about specific calendar years
- Verifying birthdays and anniversaries that fall on February 29