Leap Year Calculator

How to use the leap year calculator

1. Choose If a specific year is a leap year, type a year and press Calculate. The answer is Yes or No.
2. Choose All leap years between two years to get a count and the full list. The start year has to be later than 1582 and earlier than the end year, and the end year can go up to 10,000.
3. Choose The next leap year to see the first leap year after the current year on your device's clock.

The calculator applies the Gregorian calendar, which is why years up to 1582 are refused. A decimal such as 2024.7 is cut down to the whole year 2024.

The leap year rule

A year is a leap year, with 366 days and a 29 February, when it passes this test:

leap year = (divisible by 4 and not divisible by 100) or divisible by 400

1. Is the year divisible by 4? If not, it is a common year of 365 days.
2. If it is divisible by 4, is it also divisible by 100? If not, it is a leap year.
3. If it is divisible by 100, it is a leap year only when it is also divisible by 400.

Examples: 2024 ÷ 4 = 506 with no remainder, and 2024 is not a multiple of 100, so it is a leap year. 1900 is divisible by 4 and by 100 but not by 400, so it is a common year. 2000 is divisible by 400, so it is a leap year.

Why leap years exist

The Earth takes about 365.2422 days to go once round the Sun, measured from one March equinox to the next. A calendar of exactly 365 days falls behind by nearly a quarter of a day every year, which adds up to roughly 24 days per century and slowly drags the seasons across the months.

The Julian calendar fixed this by adding a day every fourth year, an average year of 365.25 days. That is slightly too long, so it drifted forward by one day about every 128 years. The Gregorian reform of 1582 removed three leap days from every 400 years, which is what the century rule does. A 400-year cycle therefore holds 97 leap years and 303 common years.

average Gregorian year = (400 × 365 + 97) ÷ 400 = 146,097 ÷ 400 = 365.2425 days

The remaining difference from the real year is about 0.0003 days, roughly one day in 3,000 years. A bonus property: 146,097 days is exactly 20,871 weeks, so the weekday pattern repeats every 400 years. The day of the week calculator makes use of this.

Leap years from 2024 to 2104

To find the next leap year by hand, round up to the next multiple of 4 and then check it against the century rule. After 2026 the next multiple of 4 is 2028, which qualifies. After 2096 the next multiple of 4 is 2100, which does not, so the answer jumps to 2104.

Leap days in everyday life

• A leap year has 366 days, which is 52 weeks plus 2 days. The same calendar date moves forward one weekday from one year to the next, or two weekdays when a 29 February lies in between.
• Over a four-year cycle there are 4 × 365 + 1 = 1,461 days, so about 1 person in 1,461 is born on 29 February.
• Rules for when a 29 February birthday or contract date falls in a common year differ between places and organisations. Check the local rule if it matters.
• To count days across a leap day, the days between dates calculator includes 29 February automatically, and the age calculator copes with leap-day birthdays.

Limits of the Gregorian rule

Countries did not all switch calendars in 1582. Catholic states such as Spain and Portugal changed that year, Great Britain and its colonies in 1752, and Russia in 1918. Before its own switch each place used the Julian rule, under which 1700, 1800 and 1900 were leap years. This calculator does not model that history and refuses years up to 1582.

Other calendars have their own leap rules. The Hebrew calendar adds a whole leap month in some years, and the Islamic calendar follows the Moon with years of about 354 days, so the rule on this page does not apply to them.