Leap Year Calculator
Check whether any year is a leap year using the Gregorian calendar rules.
How to use this tool
- Enter year in the fields above.
- Results update instantly as you type — or click Calculate.
- Read your is leap year? and the full breakdown beneath it.
Check whether any year is a leap year using the Gregorian calendar rules.
How it works
This tool checks whether a given year is a leap year according to the Gregorian calendar rules. A leap year has 366 days because February gains an extra day (February 29) to keep the calendar synchronized with Earth's roughly 365.25-day orbit around the sun.
The Gregorian rule has three conditions: a year is a leap year if it is divisible by 4; however, years divisible by 100 are NOT leap years unless they are also divisible by 400. So 2000 was a leap year, but 1900 was not.
Enter any year and the tool immediately tells you whether it is a leap year and which rule applies. This is useful for date arithmetic, scheduling February-29 events (like birthdays), and verifying calendar software behavior.
Historically, the Julian calendar used only the "divisible by 4" rule, which caused a gradual drift. The Gregorian reform in 1582 added the century exceptions to bring the calendar back in line with the astronomical year.
Worked example
Is 1900 a leap year?
- Enter year: 1900
- Click Check
- Result: NOT a leap year -- 1900 is divisible by 100 but not by 400
1900 is not a leap year. February 1900 had 28 days.
Common mistakes to avoid
- Assuming every year divisible by 4 is a leap year -- century years (1800, 1900, 2100) are exceptions.
- Forgetting that year 2000 WAS a leap year because it is divisible by 400.
- Using the Julian rule (divisible by 4 only) when working with dates after 1582.
Key terms
- Gregorian calendar
- The calendar system introduced in 1582 that most of the world uses today, with the three-part leap-year rule to keep the civil year aligned with the solar year.
- Century year
- A year ending in two zeros (e.g., 1800, 1900, 2000). Under the Gregorian rule, century years are leap years only if divisible by 400.
Frequently asked questions
- What is the leap year rule?
- A year is a leap year if it is divisible by 4, EXCEPT century years (divisible by 100) which must also be divisible by 400.
- Why was 1900 not a leap year?
- 1900 is divisible by 100 but not by 400, so it is not a leap year. 2000 was a leap year because it is divisible by 400.