Leap Year Check
Check whether a year is a leap year, keeping your date math, calendars and deadlines accurate and correct. Runs locally in your browser, GDPR-compliant.
Your inputs are processed in your browser and are not transmitted to our servers. Note: third-party resources (e.g. advertising and analytics from Google/Cloudflare) and an optional PayPal donation link may transfer data when loading or when clicked. Browser extensions or plugins may be able to read content that is visible in the input fields.
The result will appear here …
How to use this tool (video)
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Leap Year Check
The leap year check determines whether a given year is a leap year. Whether you are performing date calculations or wondering how many days a calendar year has, this tool gives you the clear answer.
How it works
The rule for leap years is clearly defined. A year is a leap year if it is divisible by 4, unless it is divisible by 100. Exception: If the year is divisible by 400, then it is a leap year nonetheless. Expressed as a formula: A year Y is a leap year if (Y modulo 4 equals 0 and Y modulo 100 does not equal 0) or (Y modulo 400 equals 0). For a concrete example: The year 2024 is divisible by 4 and not by 100, so it is a leap year with 366 days. The year 1900 is divisible by both 4 and 100 but not by 400, so it is not a leap year and has only 365 days. The year 2000 is divisible by 4, 100, and 400, so it is a leap year.
What the tool can and cannot do
The leap year check can test individual years or date inputs and clearly indicates whether it is a leap year. It correctly recognizes the special cases for century leap years. The tool cannot process historical calendar systems like the Julian calendar and is limited to the Gregorian calendar. It does not calculate consecutive leap years or display leap year statistics across centuries. It is a pure leap year testing utility.
Why local processing in the browser
All calculations happen directly in your browser. Your year numbers are never sent to a server. There is no upload, no server log files, and no access by third parties. You need no account and no registration. After the page loads, the leap year check works offline too because all resources are cached locally. There is no server that could be attacked and your data is not transmitted over the network.
Frequently asked questions
How does the leap year rule work?
A year is a leap year if it is divisible by 4, unless it is also divisible by 100. Exception: If the year is divisible by 400, it is still a leap year. For example, 2024 is a leap year, 1900 is not, and 2000 is.
Do I need to be online?
No, after the page has loaded once, the leap year check works offline. The required resources are cached in the browser and a flaky connection will not interrupt you.
Are my data uploaded?
No, your year numbers are never sent to a server. Everything is processed locally in your browser with no upload and no third party access.
Does every year divisible by 4 have 366 days?
No. Century years like 1900 or 2100 are divisible by 4 but not leap years because they are not divisible by 400. Only century years divisible by 400 are leap years.
Can I check multiple years at once?
Yes, you can enter different years in sequence and the leap year check will test each one individually. The calculation is instant with no waiting time.
Is the tool free to use?
Yes, the leap year check is a free tool that runs directly in your browser. There are no hidden costs or limitations.