Leap Year Calculator

What Is a Leap Year?

A leap year is a calendar year that contains an extra day — February 29 — making the year 366 days long instead of the usual 365. The extra day is added every four years to keep the calendar aligned with Earth's orbit around the Sun, which actually takes about 365.2422 days.

Without leap years, the calendar would slowly drift out of sync with the seasons. Over a century, the seasons would shift by roughly 24 days. The leap-year rule has kept the Gregorian calendar accurate to within one day for thousands of years.

Example: entering 2024 → Yes, 2024 is a leap year — divisible by 4 and not a century year, so February had 29 days and the year totaled 366 days.

How the Calculator Works

The calculator applies the standard Gregorian leap-year rule:

• If the year is divisible by 4 — it is a leap year candidate.
• If the year is also divisible by 100 — it is not a leap year (century exception).
• If the year is also divisible by 400 — it is a leap year (century exception override).

Quick mental check: 2024 ÷ 4 = 506 with no remainder, so 2024 is a leap year. 1900 ÷ 100 = 19 with no remainder but 1900 ÷ 400 leaves a remainder, so 1900 was not a leap year. 2000 ÷ 400 = 5 with no remainder, so 2000 was a leap year.

Why Leap Years Exist

A solar year — the time it takes Earth to orbit the Sun — is approximately 365 days, 5 hours, 48 minutes, and 46 seconds. That is roughly a quarter of a day longer than 365. Adding one extra day every four years (1 ÷ 4 ≈ 0.25) keeps the calendar synchronized with this astronomical reality.

The Julian calendar, introduced by Julius Caesar in 45 BC, used a simple "every 4 years" rule. But this slightly overcorrected, adding too many leap days over centuries. By 1582, the calendar had drifted about 10 days from the seasons. Pope Gregory XIII's reform introduced the modern Gregorian rule with the century exceptions, restoring alignment.

Today the Gregorian calendar is the international civil standard. Its leap-year math is accurate enough that the calendar will not drift by even one full day for over 3,000 years.

Common Uses

• Birthday planning – If you are a "leapling" born on February 29, see when your next true birthday falls
• Age calculations – Verify whether an age computation crosses a leap year (which adds an extra day to that span)
• Project schedules – Check if February 29 falls within a multi-month project timeline
• Financial year planning – Some annual contracts and tax cycles need to account for the 366th day
• Historical research – Confirm whether a particular year in the past was a leap year (after 1582 in Catholic countries; later in others)
• Trivia and curiosity – Settle bets and questions about whether 1900, 2000, or any other year had a February 29

Frequently Asked Questions