Leap Year Checker & Intercalary Rule Verifier
Verifies whether any Gregorian calendar year is a leap year with 366 days based on the 4, 100, and 400-year intercalary astronomical rules.
How This Calculation Formula is Formulated
Verifies whether a year in the Gregorian calendar contains 366 days based on the 4-year, 100-year century exception, and 400-year quad-century astronomical rules.
Variable Definitions & Measurement Units
Testing Year 2000 vs Year 1900
Explaining why 2000 was a leap year while 1900 was a common year.
The Astronomical Reason for the 400-Year Rule
Earth's orbital revolution around the Sun takes approximately 365.2422 solar days, not exactly 365.25 days. Adding a leap day every 4 years (Julian calendar) overcompensates by about 11 minutes per year.
Over 1,000 years, this causes a 7-day drift in seasons. Pope Gregory XIII reformed the calendar in 1582 by skipping leap years in century years not divisible by 400, reducing calendar error to just 1 day in 3,300 years.
Frequently Asked Questions About Leap Year Checker & Intercalary Rule Verifier
Will the year 2100 be a leap year?
No. 2100 is divisible by 100 but NOT divisible by 400, so it will be a common year with 28 days in February.
What is a leap second?
A leap second is a one-second adjustment periodically added to Coordinated Universal Time (UTC) to compensate for variations in Earth's rotational speed.
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