Leap Year Checker
Check whether any year is a leap year and understand why, with the divisibility rules explained, plus the next and previous leap years. Free, private, instant.
Last reviewed by the Radiatus Cloud team
Need this done properly for your business?
Radiatus delivers secure cloud, DevOps & compliance engineering.
Check any year for a leap year
A leap year has an extra day, and the rule for which years qualify is more subtle than most people remember. This checker tells you whether any year is a leap year and explains why, applying the full divisibility rules rather than the common oversimplification.
The rule people get wrong
Most people know a leap year is divisible by four, but the full rule has two more parts: a year divisible by 100 is not a leap year, unless it is also divisible by 400. So 1900 was not a leap year but 2000 was, which trips up many people and, famously, some software. The rule exists because the year is not exactly 365.25 days, so the simple every-four-years correction slightly overshoots and needs the century adjustments to stay accurate.
The rule, applied and explained
Everything runs in your browser, so nothing you enter is uploaded and the tool works without an account. That keeps your study material and notes private on your own machine while you learn.
Related tools
- Security Term Translator — Translate complex security jargon into business language.
- Security Myth vs Reality — Fact-check common security myths.
- Breach News Impact — Contextualize major breaches into understandable analogies.
- Config Safety Analyzer — Paste a config snippet to check for obvious safety issues.
Frequently Asked Questions
What is the full leap year rule?
A year is a leap year if divisible by four, except years divisible by 100, unless they are also divisible by 400. So 1900 was not, but 2000 was.
Why is 2000 a leap year but 1900 not?
Because both are divisible by 100, but only 2000 is also divisible by 400. The 400 exception makes it a leap year while 1900 was not.
Why does the rule have these exceptions?
Because the year is not exactly 365.25 days. The simple every-four-years rule overshoots slightly, so the century adjustments keep the calendar accurate.
Why does it matter?
Leap year mistakes cause real bugs in date calculations, so the full rule matters wherever software or planning depends on exact dates.
Is my input uploaded?
No. The check runs entirely in your browser.
Privacy & Security
All processing happens locally in your browser — nothing is uploaded.
How to Use
Enter a year to find out if it's a leap year and see the reasoning.
Disclaimer: This tool is provided "as is" without warranty of any kind. Results are for educational and utility purposes.