Leap Year Viewer.
Find the next leap year with a live countdown, check any year instantly, and browse lists of past and upcoming leap years. The Gregorian rule explained in plain English.
Leap Year Facts
Why February 29?
February was the last month in the original Roman calendar, making it the natural place to add a corrective day. Julius Caesar's Julian reform in 45 BC first introduced a leap day every four years — placed at the end of the year's last month.
The Gregorian Reform
Pope Gregory XIII introduced the Gregorian calendar in 1582 to fix the Julian system's 11-minute yearly error. The century-year exception (÷100 skip, ÷400 restore) reduced drift to ~26 seconds per year — and 10 calendar days had to be dropped overnight.
Leaplings
People born on February 29 are called "leaplings." Roughly 1 in 1,461 births fall on Leap Day — about 5 million people alive today. In non-leap years most celebrate on February 28 or March 1, depending on local tradition and jurisdiction.
97 Leap Years per 400
The Gregorian cycle has exactly 97 leap years in every 400-year period, giving an average year of 365.2425 days. Earth's true orbital period is 365.24219 days — an error of just 0.0003 days/year, or one day in roughly 3,300 years.
How to calculate leap years
The Gregorian leap year rule has three nested conditions: a year is a leap year if it is
divisible by 4, unless it is also divisible by 100, in which case it is not a leap year —
unless it is also divisible by 400, in which case it is a leap year again. In code:
(year % 4 === 0 && year % 100 !== 0) || year % 400 === 0.
Why do we need leap years?
Earth completes one orbit around the Sun in approximately 365.2422 days — not a whole number. Without adjustment, the calendar would drift about one day every four years. After a century, midsummer would fall in what the calendar calls mid-spring. Adding an extra day roughly every four years keeps the calendar aligned with the astronomical seasons.
Julian vs. Gregorian calendar
The Julian calendar (45 BC) used a simple rule: every year divisible by 4 is a leap year, giving an average year of exactly 365.25 days — about 11 minutes too long. By 1582, the Julian calendar had drifted 10 full days ahead of the solar calendar, shifting Easter away from the spring equinox. Pope Gregory XIII corrected this by dropping 10 days in October 1582 and adding the century-year exception.
Notable leap years
Year 2000 was a rare century leap year (divisible by 400), often misunderstood because 1900 — which looked similar — was not a leap year (divisible by 100 but not 400). The leap year 1752 caused Britain to switch from the Julian to the Gregorian calendar, dropping 11 days in September. Future notable leap years include 2400, the next century leap year, and 2100, 2200, and 2300, which will all be skipped.
Frequently Asked Questions
- What is the leap year rule?
- A year is a leap year if it is divisible by 4, except century years (divisible by 100), which must also be divisible by 400 to qualify. In code:
(year % 4 === 0 && year % 100 !== 0) || year % 400 === 0. - When is the next leap year?
- The next leap year after 2024 is 2028. Leap years occur every 4 years with century exceptions: 2100, 2200, and 2300 will be skipped; 2400 will be a leap year.
- Was the year 2000 a leap year?
- Yes. 2000 was a century year (divisible by 100) but also divisible by 400, making it a leap year. This is often confused with 1900, which was NOT a leap year — divisible by 100 but not by 400.
- What happens to people born on February 29?
- People born on February 29 ('leaplings') celebrate in non-leap years on either February 28 or March 1, depending on local tradition and legal jurisdiction. About 5 million people worldwide are leaplings.
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