Leap year checker
Instantly check whether a year has 366 days (a leap year, with a February 29) or 365 days, and understand the mathematical rule applied. The calculation runs locally, with no data sent.
How it works
The Gregorian calendar adds an extra day (February 29) in certain years to make up for the slight gap between the calendar year (365 days) and the actual time it takes the Earth to orbit the sun (about 365.2422 days). This tool applies the official Gregorian calendar rule to determine whether a given year is a leap year.
What exactly is the leap year rule?
A year is a leap year if it is divisible by 4, unless it is also divisible by 100, in which case it isn't, unless it is also divisible by 400, in which case it is a leap year again. In practice, 2000 was a leap year (divisible by 400), but 1900 was not (divisible by 100 but not by 400), and 2024 is one simply because it is divisible by 4 without being a multiple of 100.
Why would I need to know whether a year is a leap year?
It's useful for software development (date calculations, calendar generation, payroll or contributions based on 365/366 days), for checking a February 29 birth date, or simply out of historical or astronomical curiosity.
No data is sent to a server: the calculation runs entirely in your browser.