Leap Year Checker

The actual rule, in plain terms

A year is a leap year if it's divisible by 4 — except century years (those ending in "00"), which are only leap years if they're also divisible by 400. That's why 2000 was a leap year, but 1900 and 2100 are not. This extra rule exists because a year is really about 365.2422 days long, not exactly 365.25 — the "divisible by 400" exception corrects the small overcorrection that a plain every-4-years rule would introduce, keeping the calendar aligned with the seasons over centuries.

Working out someone's exact age and want to check if their birth year had 366 days? Use the Age Calculator.