Leap Year Calculator
A Gregorian leap year is divisible by 4, except century years must also be divisible by 400.
Enter the year to test
Enter a year to check whether it is a leap year in the Gregorian calendar. The result tells whether February has 29 days in that year.
Use this for date math, birthday checks, calendar planning and programming validation. The rule is simple, but century years are the part most people miss.
If you are checking a historical date, confirm that the Gregorian calendar is the calendar you need. Older records may use another calendar.
For modern scheduling, the Gregorian rule is usually the one people mean. The calculator is built around that everyday use case.
Leap year or common year
A leap year has 366 days instead of 365. The extra day is February 29. It keeps the calendar better aligned with Earths orbit around the sun.
If the result says the year is not a leap year, February has 28 days. Date calculations that cross February will use that shorter month.
This affects countdowns, age in total days and any date range that includes late February.
The Gregorian leap rule
In the Gregorian calendar, most years divisible by 4 are leap years. Century years are the exception. A century year must also be divisible by 400.
That means 2024 is a leap year. 1900 was not a leap year. 2000 was a leap year because it is divisible by 400.
Why 2000 passed and 1900 did not
Check 2028. It is divisible by 4 and not a century year, so it is a leap year. February 2028 has 29 days.
Check 2100. It is divisible by 4 and by 100, but not by 400. Under Gregorian rules, 2100 is not a leap year.
This example is useful because it shows why the century rule matters. A simple every four years shortcut would get 2100 wrong.
The every-four-years shortcut
The biggest mistake is stopping at divisible by 4. That works for many years, but it fails for century years such as 1900 and 2100.
Another mistake is applying the rule to every calendar system in history. This calculator uses Gregorian calendar rules, which are the standard for modern civil dates in many countries.
Also remember that a leap year changes the year length, not every month. Only February gains the extra day.
Leap Year Calculator FAQ
What is the leap year rule?
A Gregorian year is a leap year if it is divisible by 4, unless it is divisible by 100. If it is divisible by 100, it must also be divisible by 400.
So 2024 is a leap year, 1900 is not and 2000 is.
Why was 1900 not a leap year?
1900 is divisible by 100, so it needs to be divisible by 400 to remain a leap year. It is not divisible by 400.
That is why February 1900 had 28 days in the Gregorian calendar.
The year looks like it should qualify under the every four years shortcut, but the century exception removes it.
Why was 2000 a leap year?
2000 is divisible by 400, so it passes the century year exception. It was a leap year under Gregorian rules.
This is the part that makes the rule slightly more than just every four years.
It is a good test case for a calculator because both the divisible by 100 and divisible by 400 rules apply.
How often does a leap year happen?
Most leap years happen every four years. The century exceptions skip some of those years, so the long term pattern is not exactly one leap year every four years.
That small correction keeps the calendar from drifting too far over time.
Does a leap year affect age or days between dates?
Yes, if the date range crosses February 29. The extra day can change total days, countdowns and duration calculations.
Exact age still depends on birthdays, but total days lived will include February 29 when it falls in the range.
For birthday questions, leap day recognition can also depend on local or organizational rules, not only the calendar.