Leap Year Calculator
Check if any year is a leap year using Gregorian rules. See February length and leap-year facts with this free online leap year calculator tool.
How to Use
- Enter the year you want to evaluate (1-9999).
- Click Check leap year to apply Gregorian rules.
- Read yes/no result and February day count in details.
- Review which divisibility rule decided the outcome.
- Try adjacent years to see century boundary behavior.
Input Field Guide
- Year
- Four-digit (or smaller) positive year to test against Gregorian leap rules.
Understanding Your Results
The result states clearly whether the year is a leap year. Detail chips explain February length (28 vs 29 days) and cite the rule branch-divisible by 4, century exception, or 400-year exception-that determined the answer.
Features
- Gregorian leap-year rules through year 9999
- February length display
- Rule explanation in details
- Instant single-year lookup
- Copy result text
- Offline-capable after load
Formula & Calculation Logic
Leap if (year mod 4 = 0) and (year mod 100 ≠0 or year mod 400 = 0).
Real-World Use Cases
- Calendar and coding homework verification
- Date library unit test spot checks
- Genealogy around February 29 births
- Financial models spanning February
- Teaching Gregorian reform rules
Practical Examples
1900 -> not a leap year despite divisible by 4 (failed century rule).
2000 -> leap year because divisible by 400.
Benefits
- Settles century-year debates instantly
- Shows why not every multiple of 4 leaps
- No account needed
- Educational rule transparency
Tips & Best Practices
- Pair with date calculator when shifting dates across February in leap years.
- Remember age calculator handles leap-day births separately.
- Use year 2000 vs 1900 examples when teaching century exceptions.
Common Mistakes to Avoid
- Applying Julian calendar rules to modern Gregorian years.
- Assuming 2100 will be a leap year-it will not.
- Using leap check for lunar or Hebrew calendar leap months.
Frequently Asked Questions
What makes a year a leap year in this calculator?
Gregorian rule: divisible by 4, except centuries unless divisible by 400.
Is 1900 a leap year?
No. Century years must be divisible by 400.
Is 2000 a leap year?
Yes. It is divisible by 400.
Will 2100 be a leap year?
No. 2100 fails the century exception.
How many days does February have in a leap year?
29 days. Non-leap years have 28.
Does this cover Julian calendar years?
No. It applies modern Gregorian leap rules only.
Can I check BC years?
The field expects positive integers 1-9999 for CE years.
Is the year sent to a server?
No. The check runs locally.