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Worked Examples
- 1.2024 mod 4 = 0, so it could be a leap year
- 2.2024 mod 100 = 24, so the century rule does not apply
- 3.Result: 2024 IS a leap year
- 4.Days in year: 366
- 5.Days in February: 29
2024 is a leap year with 366 days. February has 29 days.
How Leap Years Work in the Gregorian Calendar
Formula
A leap year has 366 days instead of 365, with the extra day added on February 29. The Gregorian calendar uses three rules to determine leap years: (1) a year divisible by 4 is a leap year, (2) unless it is also divisible by 100, in which case it is not, (3) unless it is also divisible by 400, in which case it is a leap year. This system corrects for the fact that Earth's orbital period is approximately 365.2422 days.
Under these rules, 2000 and 2400 are leap years (divisible by 400), but 1900, 2100, 2200, and 2300 are not (divisible by 100 but not 400). Common years like 2023 and 2025 have 365 days with February having only 28 days. The Gregorian correction keeps the calendar aligned with the astronomical seasons to within one day over 3,236 years.
Common use cases:
- Verifying dates for software development
- Calendar planning and scheduling
- Historical date research
- Birthday calculations for Feb 29 babies
Frequently Asked Questions
Dr. David Park
Applied Mathematician, PhD Mathematics
David holds a PhD in Applied Mathematics from MIT. He has published research on numerical methods and computational algorithms used in engineering and scientific calculators.
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