Leap Year Checker
Leap Year Checker applies the proleptic Gregorian divisibility rule to a numeric year. Years divisible by four are usually leap years, century years must also be divisible by 400, and qualifying years contain 29 February. Historical calendar adoption is outside this arithmetic check.
Runs locally — files stay on your deviceWhy was 2000 a leap year but 1900 was not?
Both are divisible by 100, but only 2000 is also divisible by 400.
Century years are the exception to the divisible-by-four rule
A Gregorian year is leap if divisible by 4, except years divisible by 100 are common unless they are also divisible by 400.
How it works
Enter a year. The tool applies the divisibility conditions and returns whether the Gregorian year is leap or common.
Key concepts
Divisible by 400 overrides the century exception
That is why 2000 was leap while 1900 was common.
Leap years have 366 days
The additional date is 29 February.
When to use it
- Check whether February has 29 days.
- Validate a Gregorian date rule.
- Explain century-year exceptions.
When not to use it
- Do not assume the Gregorian calendar applied historically in every place.
- Do not use the result for another calendar system.
- Do not infer weekdays or dates from leap status alone.
Worked examples
Ordinary leap year
- Input
2028- Expected output
Leap year
2028 is divisible by four and not by 100.
Century exception
- Input
1900- Expected output
Not a leap year
It is divisible by 100 but not 400.
Four-hundred-year rule
- Input
2000- Expected output
Leap year
It is divisible by 400.
Common mistakes
Checking divisibility by four only
That incorrectly marks 1900 as leap. Correction: Apply both century conditions.
Assuming all calendars match
Other calendar systems use other rules. Correction: Identify the calendar first.
Applying modern dates historically without context
Gregorian adoption happened at different times. Correction: Consult historical calendar records.
Best practices
- Use integer Gregorian years.
- Remember the 100 and 400 exceptions.
- State when a historical calculation is proleptic.
Related operations and differences
Add Days to Date
Choose Add Days to Date when you need to find a future date after adding days.; use Leap Year Checker specifically for leap year.
Add Months to Date
Choose Add Months to Date when you need to add calendar months using local browser time.; use Leap Year Checker specifically for leap year.
Add Weeks to Date
Choose Add Weeks to Date when you need to add a number of weeks to a date.; use Leap Year Checker specifically for leap year.
Date Difference Calculator
Choose Date Difference Calculator when you need to count calendar days between two dates.; use Leap Year Checker specifically for leap year.
Subtract Days From Date
Choose Subtract Days From Date when you need to find an earlier date by subtracting days.; use Leap Year Checker specifically for leap year.
Subtract Weeks From Date
Choose Subtract Weeks From Date when you need to subtract a number of weeks from a date.; use Leap Year Checker specifically for leap year.
Limitations and privacy
- Uses proleptic Gregorian arithmetic.
- Does not model regional calendar adoption.
- Does not convert between calendar systems.
Dates and calculations stay in this browser and are not uploaded.
Frequently asked questions
Is every fourth year a leap year?
Usually, but century exceptions apply.
Was 2000 a leap year?
Yes.
Was 1900 a leap year?
No.
How many days are in a leap year?
366.