How Many Leap Years Have There Been Since 1900?
31 leap years fell between 1900 and 2024 — 1904, 1908, and every fourth year after. But notice what is not on that list: 1900 itself. It looks like a leap year, divisible by 4, and it wasn't one — which is exactly why people search for a list that starts there.
Is it a leap year? And list them all
Type any year to run the real three-step rule, then list every leap year in a range. Try 1900, then 2000.
Skipped century year in this range (divisible by 100 but not 400): 1900. That is the gap most people miss.
Type 1900 into the checker, then 2000. Same "divisible by 100," opposite answers — that single 400 test is the whole story of this page.
The list — and the gap at the very top
From 1904 through 2024, leap years arrive like clockwork every four years: 1904, 1908, 1912 … 2020, 2024. That is 31 of them, and the live list above will extend the run as far forward or back as you like. The next three are 2028, 2032 and 2036.
The reason the list opens at 1904 and not 1900 is the entire point of asking "since 1900." Most people assume any year divisible by 4 gets a 29 February. 1900 is divisible by 4 — and still had only 365 days. The list quietly begins with an exception.
The century rule that skipped 1900
The full Gregorian rule has three steps, not one. A year is a leap year if it is divisible by 4 — unless it is divisible by 100, in which case it is skipped — unless it is also divisible by 400, in which case it counts after all. So 1700, 1800 and 1900 were skipped, while 1600 and 2000 were kept.
This century exception exists because the simpler rule drifts. The Julian calendar, introduced by Julius Caesar in 46 BC, added a leap day every four years with no exceptions — slightly too many, by about three days every 400 years. By the 1500s the date of Easter had wandered ten days off the seasons. Pope Gregory XIII fixed it in 1582 by dropping three leap days from every 400-year cycle: the century years not divisible by 400.
Why 2000 fooled people — and some software
The year 2000 was the first century leap year since 1600. It was a leap year, because 2000 is divisible by 400. But plenty of people — and a surprising amount of code — had internalised a half-remembered rule that "century years are never leap years," and got it backwards.
In the run-up to the year 2000, this became a genuine, if minor, cousin of the Y2K bug: systems that handled the "divisible by 100" skip but forgot the "divisible by 400" exception would have treated 29 February 2000 as a non-existent date. The date was real; the assumption was the bug.
97 in 400: the maths of the fix
Drop three leap days every four centuries and a 400-year cycle contains exactly 97 leap years, not 100. That makes the average calendar year 365.2425 days long — within about half a minute of the true solar (tropical) year of roughly 365.2422 days. The leftover error is around one day every 3,000-plus years.
Britain and its colonies clung to the Julian calendar until 1752, by which point they were 11 days adrift. The Calendar Act forced the correction in one jump: Wednesday 2 September 1752 was followed by Thursday 14 September 1752, and eleven dates simply never happened.
Why "since 1900" is the sharpest way to ask
People could ask for a list of leap years since any year. They reach for 1900 because it sits at the seam — close enough to feel modern, but landing on the one recent year where the "every four years" shortcut breaks. A list starting in 1900 is really a quiet test of whether you know the century rule.
And it sets up the better trap for the future: 2100 will be skipped too, for the same reason 1900 was. Anyone alive now who assumes "2100, divisible by 4, must be a leap year" will be wrong — see exactly which seconds the calendar is fighting in seconds in a day.
Common questions
Game: leap or not?
Six years, some of them century-year traps. Trust the three-step rule, not the four-year reflex.
1900
Leap year, or not?
Sources
- Gregorian calendar reform — introduced by Pope Gregory XIII, papal bull Inter gravissimas, 1582; added the "divisible by 400" century exception.
- Julian calendar — introduced by Julius Caesar, 46 BC; leap day every 4 years with no exception, drifting ~3 days per 400 years.
- Average Gregorian year 365.2425 days vs the tropical year ≈ 365.2422 days; 97 leap years per 400-year cycle.
- British adoption — Calendar (New Style) Act 1750; 2 September 1752 was followed by 14 September 1752, dropping 11 days.
- Leap years 1900–2024 computed directly from the Gregorian rule (shown live in the checker above).
More about the calendar
Every fourth year, with three quiet exceptions a century — and 1900 was one of them.