Leap Year Checker

How the Leap Year Checker works

The leap year rules

The Gregorian formula has three parts. A year divisible by 4 is a leap year, except a year divisible by 100, which is not, except a year divisible by 400, which is. Written as a single test: the year is a leap year when it divides by 4 and either does not divide by 100 or does divide by 400.

Worked examples

For example, 2028 divides by 4 and not by 100, so it is a leap year. As a second example, 1900 divides by 100 but not by 400, so it was not a leap year, while 2000 divides by 400 and was. The next century year to skip its leap day is 2100.

Why leap years exist

The solar year is about 365.2422 days. Adding a day every four years gives an average of 365.25, which is slightly too long, so dropping three leap days every 400 years brings the average to 365.2425. That keeps the equinoxes on roughly the same dates for thousands of years.

How many leap years are there in a century?

Usually 24, because the century year itself is skipped. A century that includes a year divisible by 400, such as 2000, has 25. The table lists every leap year this century with the weekday of its 29 February.

Leap years from 2000 to 2096 and the weekday of 29 February

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