Leap Year Checker
Check if any year is a leap year instantly with our free online tool. Supports batch checking multiple years at once. 100% private, runs entirely in your browser - no data sent to servers.
What is a leap year?
A leap year is a year that has 366 days instead of the usual 365. The extra day is February 29th, which occurs once every four years in most cases.
How do you determine if a year is a leap year?
A year is a leap year if it is divisible by 4. However, century years (years ending in 00) must be divisible by 400 to be leap years. For example, 2000 was a leap year, but 1900 was not.
Why do we have leap years?
Leap years exist to keep our calendar aligned with Earth's orbit around the Sun. A solar year is approximately 365.2422 days, so we add an extra day every four years to compensate for the fractional days.
Can I check multiple years at once?
Yes, you can enter multiple years, one per line, and the tool will check each one instantly. This is useful for batch verification of historical or future dates.
Is my data safe when using this tool?
Absolutely. All processing happens locally in your browser. No data is sent to any server, and the tool works completely offline after the initial page load.
What are some examples of leap years?
Recent leap years include 2000, 2004, 2008, 2012, 2016, 2020, 2024. The next leap years will be 2028, 2032, 2036. Note that 1900 was not a leap year, but 2000 was.
Why is 1900 not a leap year but 2000 is?
This is due to the century rule: years divisible by 100 are not leap years unless they are also divisible by 400. 1900 is divisible by 100 but not 400, so it's not a leap year. 2000 is divisible by both 100 and 400, so it is a leap year.
What is the formula for calculating leap years?
The formula is: if (year % 4 == 0 && year % 100 != 0) || (year % 400 == 0), then it's a leap year. This means divisible by 4, except century years which must be divisible by 400.
Does this tool work for any year, including past and future years?
Yes, the tool works for any year in the past or future. The leap year rules apply consistently across the Gregorian calendar, which has been in use since 1582.
How accurate is this leap year checker?
The tool is 100% accurate. It uses the standard Gregorian calendar leap year rules, which are the same rules used worldwide for civil calendars.
Can I use this tool offline?
Yes, after the initial page load, the tool works completely offline. All calculations are performed locally in your browser using JavaScript.
What happens if I enter an invalid year?
The tool will display a clear error message indicating that the input is not a valid year. It accepts positive integers only.
Is there a limit to how many years I can check at once?
There is no strict limit. You can enter as many years as you need, one per line. The tool processes them instantly in your browser.
Why do some sources say leap years occur every 4 years?
This is a simplification. While most leap years occur every 4 years, the century rule (divisible by 100 but not 400) creates exceptions. For example, 1700, 1800, and 1900 were not leap years despite being divisible by 4.
How to Use Leap Year Checker
Check whether any year is a leap year, or test a whole batch of years and ranges at once. The calculation runs 100% locally in your browser — nothing is sent to any server.
- Type years into the input, one per line (e.g. 2024) or as a range like 2000-2024.
- Run the check: each year is evaluated against the leap year rules (divisible by 4; century years must be divisible by 400).
- Read the verdict for each year in the results area that starts with 'Results will appear here...'.
- Copy the list of leap years for your calendar planning or date calculations.
Century years are leap years only when divisible by 400 — 2000 was a leap year, but 1900 was not.
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