🗓️ Leap Year Checker

The Gregorian calendar determines leap years with these rules: first, a year divisible by 4 is a leap year; second, one divisible by 100 is a regular year; third, one divisible by 400 is a leap year again. For example, 2024 is divisible by 4 but not 100, so it is a leap year; 1900 is divisible by 100 but not 400, so it is a regular year; and 2000 is divisible by 400, so it is a leap year.

This tool lists every leap year in the 100-year block containing the entered year (e.g. 2000-2099) in one view, and also calculates the nearest next and previous leap years relative to the entered year. It is handy for quickly checking how many years until the next leap year in a project timeline, or when the next real birthday falls for someone born on February 29.

Earth takes about 365.2422 days to orbit the Sun. Fixing a year at 365 days accumulates about 0.2422 days of error every year, so an extra day (February 29) is added every four years to correct it. Adding exactly one day every four years would over-correct slightly, so years divisible by 100 skip the leap year, while years divisible by 400 restore it as an exception.