Leap Year Checker

The Leap Year Checker tells you whether a given year is a leap year — one with 366 days instead of 365, with February 29th added to keep the calendar aligned with Earth's orbit around the Sun. Because a solar year is about 365.2422 days, inserting an extra day roughly every four years corrects the drift that would otherwise accumulate and push the seasons out of sync with the calendar.

The rule it applies is the Gregorian calendar's: a year is a leap year if it is divisible by 4, except for century years, which must also be divisible by 400. So 2000 and 2400 are leap years, but 1900 and 2100 are not, even though all are divisible by 4. This 400-year refinement is what makes the Gregorian calendar far more accurate than the older Julian rule, which counted every fourth year without exception.

Knowing whether a year is leap matters for scheduling, age and date arithmetic, payroll periods, and software that must handle February 29th correctly. Date bugs around leap years are a recurring source of errors in spreadsheets and code, so a quick checker is useful when validating data or planning events that land near the end of February.

Practical tips: people born on February 29th ("leaplings") typically observe their birthday on February 28th or March 1st in common years; and when computing date differences spanning a leap year, account for the extra day. Use this alongside a Week Number Calculator or Time Duration Calculator when leap-year edge cases affect your date math.