Leap Year Checker

Most people learn that a leap year is any year divisible by 4, and that shortcut is exactly what trips them up: 1900 was not a leap year and 2100 will not be either. When you need to confirm whether February has 29 days in a given year, maybe to check a birthday, close out a day count, or test date validation in some code, type the year and you get the answer instantly, along with the next ten leap years after it.

The full Gregorian rule has three steps: a year is leap if divisible by 4, except century years, which are leap again only when divisible by 400. That is why 2000 had a February 29 and 1900 did not. The reason is the solar year lasting about 365.2425 days: adding a day every 4 years, the old Julian scheme, overshoots the mark, and dropping 3 leap days every 400 years corrects almost all of the drift.

The list of upcoming leap years is handy for anything tied to February 29, like software test cases or annual closing routines. One caveat: the tool applies the Gregorian rule to any number you type, but before 1582 the Julian calendar was in force (a leap year every 4 years, no exceptions), so for historical years the answer may not match the calendar actually in use. Everything runs in your browser; nothing is sent to a server.