Leap Year Calculator
Check if any year is a leap year, explore next and past leap years, and understand the Gregorian 400-year rule.
2026 is NOT a leap year because it is not evenly divisible by 4.
2028
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What Is a Leap Year Calculator?
A leap year calculator determines whether a given calendar year contains 366 days instead of 365, with February 29 as the leap day. It implements the complete three-part Gregorian rule designed to keep our calendar synchronized with Earth’s astronomical orbit around the Sun.
How to Use This Calculator
- Enter any year (e.g. 2024, 2028, or historical years like 1900 or 2000).
- Instantly see whether the year is a leap year or common year.
- Read the specific mathematical rule explanation and view the adjacent leap years.
Gregorian Leap Year Algorithm
\text{LeapYear}(Y) = (Y \equiv 0 \pmod 4 \land Y \not\equiv 0 \pmod{100}) \lor (Y \equiv 0 \pmod{400})A year is a leap year if divisible by 4, unless it is divisible by 100, unless it is also divisible by 400.
Worked Example
Scenario: Why was the year 2000 a leap year, but 2100 will NOT be a leap year?
Year 2000 is divisible by 100, but ALSO divisible by 400 (2000 / 400 = 5) -> Leap Year!
Year 2100 is divisible by 4 and 100, but NOT divisible by 400 (2100 / 400 = 5.25) -> Common Year (365 days).
Tips & Key Notes
- Earth takes approximately 365.2422 days to orbit the Sun, creating a ~0.2422 day discrepancy each year.
- Without leap years, every 100 years the calendar would drift by about 24 days, causing summer to eventually fall in December in the Northern Hemisphere.
- People born on February 29 are called "leaplings" or "leapers" and celebrate on February 28 or March 1 in non-leap years.
Frequently Asked Questions
What are the 3 rules for a leap year?
1. The year must be divisible by 4. 2. If divisible by 100, it is NOT a leap year, UNLESS: 3. It is also divisible by 400.
Why was 1900 not a leap year?
1900 is divisible by 4 and 100, but not divisible by 400 (1900 ÷ 400 = 4.75), so it was a common year with 365 days.
When is the next leap year?
Following 2024, the next leap years are 2028, 2032, 2036, 2040, and 2044.
How many days are in February during a leap year?
February has 29 days in a leap year, compared to 28 days in a common year.
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