Leap Year Calculator

The calculator has two inputs. Year to check accepts any whole year from 1 to 9999. Years ahead to list controls how far forward the list of upcoming leap years reaches, in steps of 4, from 4 up to 100 years.

Enter 2026 with the default look-ahead of 20 years. The headline result reads No, and the explanation line names the exact rule that decided it: 2026 is not divisible by 4. Below that, the calculator reports 365 days in this year, a next leap year of 2028 and a previous leap year of 2024. The upcoming list shows 2028, 2032, 2036, 2040 and 2044, every leap year that falls within 20 years of 2026.

If the year you enter is itself a leap year, it appears at the start of the upcoming list, while the next and previous fields always look strictly after and strictly before it. Enter 2024 and the list starts at 2024, but the next leap year is still reported as 2028 and the previous as 2020. That distinction matters when you are asking "how long until the next February 29" in a year that already contains one.

The bar chart underneath is fixed rather than tied to your input: it counts leap years in four centuries, as the next section explains.

The whole calculator rests on one test, applied in this order:

• If year mod 400 = 0 → leap year (for example 2000 and 2400).
• Otherwise, if year mod 100 = 0 → common year, even though the year is divisible by 4 (1700, 1800, 1900, 2100).
• Otherwise, if year mod 4 = 0 → leap year (2024, 2028).
• Otherwise → common year (2025, 2026).

A leap year has 366 days because February gains a 29th day; every other year has 365. The explanation line on the page reports whichever branch fired, so you can see why a year passed or failed rather than just the verdict.

Next and previous leap year are found by stepping one year at a time forward (or backward) and applying the same test until it passes. That is slower than rounding to the nearest multiple of 4, but it cannot be fooled by a skipped century year, because the century rule is tested at every step.

Leap years per century counts every year in a 100-year window that passes the test. Across a full 400-year cycle the rule produces 97 leap years, not 100, which puts the average calendar year at 365.2425 days. The chart shows the result: the 18th (1701-1800), 19th (1801-1900) and 21st (2001-2100) centuries each hold 24 leap years because their closing year is skipped, while the 20th century (1901-2000) holds 25 because it ends on 2000, a year divisible by 400.

The century rule is where simple "divisible by 4" checks go wrong. Enter 1900: it divides by 4 (475) and by 100 (19) but not by 400 (4.75), so the calculator returns No, 365 days, and reports 1896 as the previous leap year and 1904 as the next. Now enter 2000: it divides by 4, by 100 and by 400 exactly (5), so it returns Yes, 366 days, with 1996 before it and 2004 after it. Two years that look identical to a divide-by-4 test land on opposite sides of the rule.

The same rule produces the longest wait anyone alive today is likely to see for a February 29. Suppose you are planning from a date in 2097 and want the next leap year. Enter 2097: the previous leap year is 2096, but the next one is 2104, not 2100, because 2100 is a century year that fails the 400 test. With the look-ahead at 20 years, the upcoming list reads 2104, 2108, 2112 and 2116. Enter 2096 itself and the list reads 2096, 2104, 2108, 2112, 2116, showing an eight-year gap where you would normally expect four.

Any schedule, subscription or contract that assumes "every fourth year" will be off by one leap day in 2100. That is why software should call a real leap-year test rather than checking year mod 4 alone.

A solar year (equinox to equinox) lasts about 365.2422 days. A calendar with no leap years at all would slip against the seasons by roughly 24 days per century (0.2422 × 100). The Julian calendar fixed most of that with a leap day every 4 years, giving an average of 365.25 days, but that overcorrects by about 0.0078 days a year, or one full day roughly every 128 years. By the 16th century the spring equinox had drifted about ten days earlier on the calendar.

The Gregorian reform of 1582 removed the excess by dropping three leap days every 400 years: the century years not divisible by 400. That brings the average year to 365.2425 days, about 26 seconds longer than the solar year, an error that takes thousands of years to add up to a single day. Countries switched at different times; Britain and its colonies did not adopt the Gregorian calendar until 1752.

Someone born on February 29 has a birthday that exists on the calendar in only one year in four, and anyone born on February 29, 2096 will wait eight years for the next one. There is no single universal rule for which date stands in for it in a common year: different record systems and jurisdictions use February 28 or March 1, and the choice can matter for anything tied to an exact birthdate, from age-of-majority rules to licence renewals. If births were spread evenly across the calendar, the chance of a February 29 birthday would be 1 in 1,461 over a four-year span, or about 1 in 1,506 once the Gregorian century skips are counted (97 leap days in 146,097 days).

Leap years also shift everything after February by one day. In a leap year, March 1 is day 61 of the year rather than day 60, a 12-month date span that crosses February 29 contains 366 days, and interest or payroll calculations that use actual day counts pick up the extra day.

The calculator applies the Gregorian rule to every year you enter, including years before 1582. Historians call that the proleptic Gregorian calendar. It is the right convention for software and for ISO 8601 dates, but it does not match what people actually wrote at the time: a document dated in England in 1700 used the Julian calendar, where 1700 was a leap year. Converting historical dates between the two calendars needs a dedicated conversion, not this test.

It does not handle other calendar systems, such as the Julian calendar still used for some Orthodox church feasts, or the Hebrew, Islamic and Chinese calendars, which add leap months rather than a single leap day. It accepts years from 1 to 9999 only, with no year 0 and no BCE years. It also says nothing about leap seconds, which are occasionally inserted into clock time and are unrelated to the calendar leap day.

If you need the leap day accounted for in a real date span, the Date Calculator adds or subtracts days, weeks and months across February 29 correctly, and the Days Until Calculator counts down to an event that may sit on the far side of one. The Day of Year Calculator shows the ordinal day shifting by one after February in a leap year. For exact ages, including the February 29 birthday case, use the Age Calculator, and the Chronological Age Calculation guide walks through how leap years affect year, month and day borrowing.