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Leap year checker

Enter a year to find out whether it is a leap year and why.

How Leap year checker works

Leap Year Checker tells you whether any year is a leap year and explains exactly why, using the Gregorian rule. The rule has three parts: a year is a leap year if it is divisible by 4; except that century years (divisible by 100) are not leap years; except that years divisible by 400 are leap years again. So 2000 was a leap year (divisible by 400), 1900 was not (divisible by 100 but not 400), and 2024 is (divisible by 4, not a century). The check runs locally in your browser with no server contact.

The tool also shows the nearest preceding and following leap years so you can orient yourself in the leap year cycle. The cycle is almost always 4 years, but it skips at century years that are not divisible by 400. The last such skip was 1900, and the next will be 2100. Between those exceptions the pattern is regular: 2020, 2024, 2028, 2032 and so on.

Written by Bastien Sulyan

How to use Leap year checker, step by step

  1. Type or select the year you want to check.
  2. Read the yes/no answer and the explanation of which rule applies.
  3. Check the nearest previous and next leap years listed below.

Common use cases

  • A developer building a date validation function needs to verify the exact Gregorian leap year rule before coding it.
  • Someone born on 29 February wants to know how many actual birthdays they have had.
  • A financial system calculates daily interest and needs to confirm whether a specific year has 365 or 366 days.
  • A calendar designer needs to identify all leap years in a 20-year range to allocate the extra day correctly.

Frequently asked questions

What is the full Gregorian leap year rule?

A year is a leap year if: (1) it is divisible by 4, AND (2) it is not divisible by 100, OR (3) it is divisible by 400. The three conditions in combination mean that 97 out of every 400 years are leap years, giving an average year length of 365.2425 days, close to the actual solar year of approximately 365.2422 days.

Was the year 2000 a leap year?

Yes. 2000 is divisible by 400, so it satisfies condition 3 and is a leap year. This confused some software systems that only implemented the simpler 'divisible by 4' rule.

Will 2100 be a leap year?

No. 2100 is divisible by 100 but not by 400, so it fails condition 2 and is a common year of 365 days. The previous non-leap century year was 1900.

Does the leap year calculation happen on a server?

No. The rule is three integer divisibility checks that run entirely in the browser. The year you enter is not transmitted; it is evaluated locally and the result shown without any network activity.

How many days does a leap year have?

366. The extra day is 29 February, added to the shortest calendar month. All other months retain their normal length.

Does this tool apply to the Julian calendar as well?

No. The Julian calendar has a simpler rule: every year divisible by 4 is a leap year, with no century exception. This tool implements only the Gregorian rule, which is the standard civil calendar used worldwide today.

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