Is It a Leap Year?

Check Any Year

Famous Test Years

The years that best illustrate the rule — including the tricky century cases.

Leap Year Lookup Table

Want the day of the week for a leap day? Try the Day of the Week calculator.

The Gregorian Leap Rule

Calendar Accuracy Reference

No saved years yet. Tap "Save to history" to remember up to eight checks.

How to Check a Leap Year

1. Type any year into the input — the verdict stamp flips to YES or NO instantly as you type.
2. Read the decision flow: the first test checks divisibility by 4, the second by 100, the third by 400, with a green check or red cross for each.
3. Follow the logic line at the bottom of the flow — ÷4 ✓ → ÷100 ✗ → ÷400 ✓ — to see exactly which clause decided the verdict.
4. Tap a nearby leap year chip to jump to it, or use the famous test years (1900, 2000, 2100) to see the century exceptions in action.
5. Save the result to your history and watch the live countdown to the next February 29 at the top of the page.

Why Leap Years Exist

In 2026, a payroll administrator finalising a leap-year-aware salary accrual, a developer writing a date-validation unit test, and a curious nine-year-old who wants to know if they can have a real birthday party next February all ask the same one-word question: is it a leap year? This tool answers instantly with a giant YES or NO stamp, then shows exactly why by walking the year through the three divisibility tests that define the Gregorian rule.

A leap year exists because Earth does not orbit the Sun in a whole number of days. One tropical year is about 365.2422 days — roughly 365 days, 5 hours, 48 minutes, and 45 seconds. Ignoring that quarter-day causes the calendar to drift against the seasons by almost a full day every four years, which is why the Julian calendar, introduced by Julius Caesar in 46 BC on the advice of the astronomer Sosigenes of Alexandria, added one extra day every fourth year.

The Julian rule of a leap year every four years overcorrects slightly: it assumes a year of exactly 365.25 days, which is about 11 minutes too long. Over centuries those minutes accumulated, and by the 1500s the spring equinox had slipped ten days from its intended date of March 21, throwing off the calculation of Easter. Pope Gregory XIII fixed this with the Gregorian reform of 1582, dropping ten days that October (Thursday 4 October was followed directly by Friday 15 October) and tightening the leap rule.

The Gregorian rule is the one this checker implements: a year is a leap year if it is divisible by 4, except years divisible by 100, unless they are also divisible by 400. So 2024 is a leap year (divisible by 4, not by 100). The year 1900 was not a leap year (divisible by 100 but not by 400). The year 2000 was a leap year (divisible by 400). This three-step test reduces the average calendar year to 365.2425 days, leaving an error of only about one day in 3,030 years.

The intercalary day itself, February 29, lands in February for a historical reason rooted in the early Roman calendar, where February was the last month of the year and the natural place to make adjustments. People born on February 29 are called leaplings or leap-year babies; there are roughly five million of them worldwide, and many celebrate on February 28 or March 1 in common years. The odds of being born on a leap day are about one in 1,461.

The Gregorian calendar is now the global civil standard, formalised in the modern era through ISO 8601, the international date and time standard that defines a proleptic Gregorian calendar for years before 1582 and codifies the same divisible-by-4-except-by-100-unless-by-400 rule. Because computers everywhere implement ISO 8601, the same leap-year logic governs spreadsheet date math, database timestamps, and the date-validation routine in nearly every programming language.

Even the Gregorian calendar is not perfect: its 365.2425-day average is about 27 seconds longer than the true tropical year, accumulating to roughly one extra day every 3,030 years or so. Some astronomers have proposed dropping a leap day around the year 4000 or 8000, though no such rule is official. For all practical scheduling, finance, and software purposes today, the three-test Gregorian rule this tool uses is exact, which is why it underpins everything from leap-year payroll to the February 29 countdown shown below.