Three rules decide whether a year has 366 days. Enter any year to check, list all leap years in a range, or find the nearest leap year from a reference point.
1999 - Leap Year or Not?
Three rules decide whether a year has 366 days. Enter any year to check, list all leap years in a range, or find the nearest leap year from a reference point.
Is 1999 a leap year? Three rules: (1) divisible by 4 = leap year, (2) BUT divisible by 100 = not a leap year, (3) UNLESS also divisible by 400 = leap year. That is why 1900 was not a leap year but 2000 was. Enter any year and the calculator tells you instantly, plus shows the next 10 leap years from that date.
Parameters
Enter data for calculations
💡 Fill in all required fields to unlock the calculate button
Three rules, one calendar quirk
A leap year adds one extra day - February 29 - to keep the calendar aligned with Earth's orbit around the Sun. The Gregorian calendar uses three stacking rules to decide which years get that extra day. This calculator applies all three rules instantly: check a single year, scan an entire range, or find the leap year closest to any reference point.
How to use the leap year calculator - step by step
- Calculator mode - choose "Check a year" for a single year, "List leap years" for a range, or "Nearest leap year" to search from a reference point.
- Year / range / reference - enter the year(s) depending on your chosen mode. Valid range: 1-9999.
- Read the result - you get the answer with a full explanation of which divisibility rule applies.
The Gregorian leap year rules
| Rule | Condition | Leap? | Example |
|---|---|---|---|
| Rule 1 | Divisible by 4 | Yes | 2024, 2028, 2032 |
| Rule 2 | BUT divisible by 100 | No | 1900, 2100, 2200 |
| Rule 3 | UNLESS divisible by 400 | Yes | 1600, 2000, 2400 |
Why do we need leap years?
Earth takes approximately 365.2422 days to orbit the Sun. A standard calendar year of 365 days falls short by about 0.2422 days (roughly 5 hours 48 minutes 45 seconds). Without correction, the calendar would drift by one full day every four years. After a century, seasons would shift by nearly 25 days.
Notable leap year facts
| Year | Leap? | Why |
|---|---|---|
| 1900 | No | Divisible by 100 but not by 400 (Rule 2) |
| 2000 | Yes | Divisible by 400 (Rule 3 overrides Rule 2) |
| 2024 | Yes | Divisible by 4, not by 100 (Rule 1) |
| 2100 | No | Divisible by 100 but not by 400 (Rule 2) |
| 2400 | Yes | Divisible by 400 (Rule 3) |
Practical examples
Enter 2028. Result: YES, leap year. 2028 / 4 = 507 (whole number), not divisible by 100. February 2028 has 29 days.
Enter 1900. Result: NO, not a leap year. Even though 1900 / 4 = 475, it is also divisible by 100 and not by 400. Rule 2 wins.
Range 2020-2040. Result: 6 leap years - 2020, 2024, 2028, 2032, 2036, 2040. That is 28.6% of the range.
Reference year 2023. Previous: 2020 (3 years back). Next: 2024 (1 year ahead).
Enter 2000. Result: YES, leap year. This is the Rule 3 exception - divisible by 400, so it overrides Rule 2.
FAQ
Related tools
Day of Year Calculator
Find the ordinal day number (1-366) for any date - Open calculator
Date Difference Calculator
Calculate the exact gap between two dates in years, months and days - Open calculator
Age Calculator
Calculate your exact age from date of birth - Open calculator
Minutes to Hours Converter
Convert minutes to HH:MM format or hours back to total minutes - Open calculator
See also
Calculator verified by the LiczGrupa.pl team
Content, formulas and results have been reviewed for accuracy and relevance by our team of specialists.
Reviewed by: Natalia Skrzek