Check whether any year from 1 AD to 9999 is a leap year. Understand the three-rule Gregorian formula, why leap years are needed, and find every upcoming leap year.
A year is a leap year if it satisfies ALL of these rules:
Examples: 2024 ✅ (÷4) · 2026 ❌ (not ÷4) · 1900 ❌ (÷100, not ÷400) · 2000 ✅ (÷400) · 2028 ✅ (÷4, not ÷100)
Suggested subject: A calendar open to February showing the 29th date circled or highlighted, OR a frog (the leap year symbol) next to a calendar
Recommended size: 860 × 440 px | Alt text: "February calendar showing the 29th leap day highlighted in green, representing a leap year"
Subject: Earth orbiting the Sun — an illustration or long-exposure astrophotography showing the solar orbit concept
Size: 420 × 320 px
A leap year is a calendar year that contains one extra day — 29 February — giving it 366 days instead of the standard 365. The extra day is added to keep our calendar synchronised with Earth's actual orbit around the Sun.
The problem is simple astronomy: Earth takes approximately 365.2422 days to orbit the Sun (a tropical year). A calendar with exactly 365 days falls behind the solar year by about 5 hours 48 minutes and 45 seconds each year. Without correction, the calendar would drift — after 100 years, the seasons would be about 24 days off. The summer solstice would no longer fall in June.
The leap year correction adds approximately 0.25 days per year (1 day every 4 years) to compensate — but with the century-year exceptions to avoid over-correcting.
2024 ÷ 4 = 506 ✓ → candidate1900 ÷ 100 = 19 → NOT a leap year2000 ÷ 400 = 5 ✓ → IS a leap yearIn pseudocode: isLeap = (year % 4 == 0 && year % 100 != 0) || (year % 400 == 0)
| Year | ÷4? | ÷100? | ÷400? | Leap Year? |
|---|---|---|---|---|
| 1900 | ✓ | ✓ | ✗ | ✗ No |
| 1904 | ✓ | ✗ | — | ✓ Yes |
| 2000 | ✓ | ✓ | ✓ | ✓ Yes |
| 2024 | ✓ | ✗ | — | ✓ Yes |
| 2026 | ✗ | — | — | ✗ No |
| 2027 | ✗ | — | — | ✗ No |
| 2028 | ✓ | ✗ | — | ✓ Yes |
| 2032 | ✓ | ✗ | — | ✓ Yes |
| 2100 | ✓ | ✓ | ✗ | ✗ No |
| 2400 | ✓ | ✓ | ✓ | ✓ Yes |
Julius Caesar introduced the leap year to Rome in 46 BCE, acting on advice from the Egyptian astronomer Sosigenes of Alexandria. The Julian calendar added a leap day every 4 years without exception — a slight overcorrection, adding approximately 11 extra minutes per year.
By 1582, the Julian calendar had drifted about 10 days ahead of the solar year. Pope Gregory XIII reformed the calendar by skipping 10 days (Thursday 4 October was followed by Friday 15 October 1582) and introducing the century-year exception. The Gregorian calendar reduces the error to approximately 26 seconds per year — it will take about 3,300 years to drift one day.
Britain (and its colonies) adopted the Gregorian calendar in 1752, skipping 11 days. By the time Australia was first colonised in 1788, the Gregorian leap year rules were fully in place. The Gregorian calendar is now the universal civil calendar.
People born on 29 February are sometimes called leaplings or leap day babies. They have a genuine calendar birthday only every 4 years. Legal and administrative treatment of a 29 February birthday in non-leap years varies:
Our Age in Days calculator handles leap years automatically, giving you your exact age including every 29 February you've lived through.
Calculate Age in Days →A leap year is a calendar year with 366 days instead of the usual 365. The extra day (29 February) is added to keep the calendar synchronised with Earth's ~365.2422-day orbit around the Sun.
Three rules: (1) Divisible by 4 → leap year. (2) But if divisible by 100 → NOT a leap year. (3) Unless also divisible by 400 → IS a leap year. Code: (y%4==0 && y%100!=0) || y%400==0
No. 2026 ÷ 4 = 506.5 (not exact). 2026 is not divisible by 4, so it is not a leap year. The next leap year is 2028.
Yes. 2028 ÷ 4 = 507 (exact). 2028 is not a century year, so only Rule 1 applies. 29 February 2028 exists.
Yes. 2000 is divisible by both 100 and 400, satisfying Rule 3. 2000 had a 29 February. However, 1900 was NOT a leap year (divisible by 100 but not 400).
2028, 2032, 2036, 2040, 2044. All are divisible by 4 but not by 100.
Earth takes ~365.2422 days to orbit the Sun. Without a correction, the calendar drifts about 1 day every 4 years. Julius Caesar introduced leap years in 46 BCE; Pope Gregory XIII refined the formula in 1582 with the century-year exception.
Under the Acts Interpretation Act 1901, a person born on 29 February is taken to have been born on 1 March in non-leap years for Commonwealth legislation purposes.