How leap year checker works
A leap year has 366 days instead of 365, with an extra day on 29 February, to keep the calendar aligned with the solar year. Under the Gregorian calendar the rule is: a year is a leap year if it is divisible by 4, except that years divisible by 100 are not leap years unless they are also divisible by 400.
So 2024 is a leap year (divisible by 4, not by 100). 1900 is not a leap year (divisible by 100 but not by 400). 2000 is a leap year (divisible by 400). The 400-year exception corrects for the fact that a solar year is about 365.2425 days, not exactly 365.25.
Enter a year and the tool tells you whether it is a leap year and why. Use it for date calculations, calendar apps, scheduling recurring events, and checking whether 29 February exists in a given year.
Frequently asked questions
What are the leap year rules?
A year is a leap year if it is divisible by 4, unless it is divisible by 100 — in which case it must also be divisible by 400. So 2024 is leap, 1900 is not, and 2000 is.
Why is 1900 not a leap year?
Because it is divisible by 100 but not by 400. The 400-year exception exists because a solar year is about 365.2425 days, so a 100-year rule alone would over-correct.
How often does 29 February occur?
Usually every four years, but with the century exception. Across 400 years there are exactly 97 leap years, giving an average year length of 365.2425 days.
Does this work for years before 1582?
The Gregorian rules apply from 1582 onward. For historical dates before that, the Julian calendar was used, where every fourth year is a leap year with no 400-year exception. This tool applies the modern Gregorian rule to any integer year you enter.
