Leap Year Checker

Check whether any year is a leap year, with the reason and the next and previous leap years.

What is the Leap Year Checker?

A leap year has 366 days, with 29 February added to keep the calendar aligned with the solar year.

How does it work?

Gregorian rule: a year is a leap year if it is divisible by 4, except years divisible by 100, unless also divisible by 400.

Formula

Leap ⇔ (year mod 4 = 0 and year mod 100 ≠ 0) or year mod 400 = 0

Example

2028 is a leap year. 1900 was not (divisible by 100 but not 400). 2000 was (divisible by 400).

Frequently asked questions

Why do we need leap years?

A solar year is about 365.2422 days. Adding a day every four years, with century exceptions, keeps seasons aligned with dates.

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