Leap Years Explained: Why February 29 Exists
The 365.2422-day problem, the divisible-by-4 rule and its 100/400 exceptions, the next leap years, and other calendars' leap strategies.
A year is not 365 days — Earth needs 365.2422 days to orbit the sun. Without correction, the calendar would drift one day off every four years, and in 730 years July would be mid-winter. Leap days are the patch: 2028 is a leap year, with February 29 falling on a Tuesday.
The Gregorian rule
- Every year divisible by 4 is a leap year — 2024, 2028, 2032
- …except years divisible by 100: 1700, 1800, 1900, 2100 are not leap years
- …except years divisible by 400, which are: 1600, 2000, 2400
The nested exceptions tune the average year to 365.2425 days — just 26 seconds longer than the true year. The Gregorian calendar will remain accurate to within a day for roughly 3,000 years.
Upcoming leap years
| Year | Leap? | February 29 falls on |
|---|---|---|
| 2026 | No | — |
| 2027 | No | — |
| 2028 | Yes | Tuesday |
| 2029 | No | — |
| 2032 | Yes | Sunday |
| 2100 | No (divisible by 100, not 400) | — |
Why the drift matters
The Julian calendar, in force for 1,600 years, added a leap day every 4 years without the century exceptions — an average of 365.25 days. By 1582 the equinox had drifted 10 days earlier than the church's spring reference. Pope Gregory XIII deleted 10 days that October (Thursday the 4th was followed by Friday the 15th) and installed the 100/400 rules. This is also why the Orthodox churches' fixed feasts still sit 13 days later on the Gregorian calendar.
Other calendars, other leaps
- Islamic (Hijri): purely lunar, no leap days at all — the year is simply ~11 days shorter
- Chinese calendar: leap months — a whole extra month inserted about every 3 years
- Hebrew calendar: 7 leap months per 19-year cycle, keeping holidays seasonal
Curious what day of the week any date falls on? Every week archive page lists all seven dates with weekdays, for any week of 2024–2027.
Frequently asked questions
Is 2026 a leap year?
No — 2026 is not divisible by 4. The next leap year is 2028, when February 29 falls on a Tuesday.
Why is 2100 not a leap year?
Years divisible by 100 skip the leap day unless they are also divisible by 400. 2000 was a leap year; 2100, 2200 and 2300 will not be.
What happens if we never had leap years?
The calendar would drift about one day per four years — roughly 24 days per century — until the seasons and the calendar months completely decoupled.