Leap Year Calculator
Check if any year is a leap year and see upcoming leap years.
2026
is not a leap year
365 days (February has 28 days)
Rule breakdown
✗ Not divisible by 4 → not a leap year
Nearby Leap Years
Leap Year Rules
The Gregorian calendar, introduced by Pope Gregory XIII in 1582, uses three rules to determine leap years:
- If the year is divisible by 4, it might be a leap year
- If also divisible by 100, it is not a leap year
- If also divisible by 400, it is a leap year
Examples: 2000 was a leap year (÷400), 1900 was skipped (÷100 but not ÷400), 2024 is a leap year (÷4, not ÷100).
Why Leap Years Exist
Earth's orbital period is approximately 365.2422 days. Without leap years, the calendar would drift ~1 day every 4 years, eventually shifting seasons. The Gregorian correction (skipping 3 leap years every 400 years) keeps the average year length at 365.2425 days — accurate to within 1 day per 3,236 years. Over very long timescales, further calendar reform may be needed, but the ÷4/÷100/÷400 rules remain the accepted standard for the foreseeable future.
Programming Considerations
Feb 29 validation
Date inputs must reject Feb 29 in non-leap years
Day-of-year offset
Mar 1+ day numbers shift by 1 in leap years
Age calculation
People born Feb 29 — when is their birthday?
Recurring events
Annual events on Feb 29 need fallback logic
Sources
- The Science of Leap Year — Smithsonian National Air and Space Museum
- The Science of Leap Day — University of Arizona