Leap Year Checker

How it is calculated

The tool applies the Gregorian rule to the year you enter: leap = (year mod 4 = 0 and year mod 100 ≠ 0) or (year mod 400 = 0). A leap year has 366 days, any other year has 365. It also finds the next leap year after the one entered by counting upward until the rule is true. Decimals are cut to a whole year, so 2024.9 is read as 2024. The rule is applied to every year, including those before the Gregorian calendar was adopted in 1582 and years such as 0, so for old historical dates it does not match the Julian calendar then in use, in which every fourth year was a leap year. Adoption dates differed by country.

Common mistakes

• Using "divisible by 4" alone. Century years such as 1900 and 2100 are not leap years.
• Forgetting the exception to the exception: 2000 and 2400 are leap years because they are divisible by 400.
• Applying the Gregorian result to years before 1582. In the older Julian calendar, 1500 was a leap year, though this tool reports it as not.
• Entering a two-digit year such as 24. It is read as the year 24, not 2024.
• Assuming the "next" year includes the year you entered. The next leap year is always later than the one typed.