Leap Year Calculator

A year is a leap year if it is divisible by 4, except century years (those divisible by 100), which are leap years only when they are also divisible by 400. In short: divisible by 4, not by 100, unless also by 400. For example, 2024 is a leap year, 1900 is not, and 2000 is.

Both years are divisible by 4, so the simple rule would call them leap years. The century exception steps in: a year divisible by 100 is a leap year only if it is also divisible by 400. 1900 is divisible by 100 but not 400, so it is a common year, while 2000 is divisible by 400 and stays a leap year.

February has 29 days in a leap year and 28 days in a common year. The extra day, February 29, is added to keep the calendar year aligned with the solar year. This makes a leap year 366 days long instead of the usual 365.

Earth takes about 365.2422 days to orbit the Sun, slightly more than 365 days. Adding one day every four years compensates for most of that drift. The century and 400 year exceptions fine tune the average year length to about 365.2425 days, which keeps the calendar accurate to within one day over roughly 3,000 years.

It applies the Gregorian rule to any year you enter, including years before the calendar was adopted in 1582. This is called the proleptic Gregorian calendar and is the convention used by ISO 8601. Historical dates recorded under the older Julian calendar followed a simpler every fourth year rule and can differ from these results.

Leap years normally occur every four years, so after a leap year the next one is four years later. The calculator lists the next and previous leap years around the year you enter, and it correctly skips century years such as 2100 that break the four year pattern.