Is it Leap Year?

The Leap Year Checker determines whether any year is a leap year using the Gregorian calendar rules. It features three modes: check a single year with a visual step-by-step rule test, find all leap years within a custom range, or discover the next and previous leap years from any year. An interactive calendar grid shows leap year patterns at a glance.

What is a Leap Year?

A leap year is a calendar year with 366 days instead of the usual 365. The extra day, February 29, compensates for the fact that Earth's orbit around the Sun takes approximately 365.2422 days — not a neat 365. Without this correction, the calendar would drift by about 24 days every century, eventually causing summer months to fall in winter.

Leap Year Rules (Gregorian Calendar)

The algorithm for determining leap years involves three simple divisibility tests applied in order:

1. Divisible by 4? — If the year is NOT divisible by 4, it is NOT a leap year. (e.g., 2023, 2025, 2027)
2. Divisible by 100? — If divisible by 4 but NOT by 100, it IS a leap year. (e.g., 2024, 2028, 2032)
3. Divisible by 400? — If divisible by 100, it is a leap year ONLY if also divisible by 400. (e.g., 2000 ✓, 1900 ✗)

Century Year Examples

Century years are the trickiest part of leap year rules. Here are the key examples:

How Many Leap Years Per Century?

Most centuries contain 24 leap years. However, centuries whose final year (the "00" year) is divisible by 400 contain 25 leap years. For example, the 20th century (1901–2000) had 25 leap years because 2000 was a leap year, while the 21st century (2001–2100) will have only 24 because 2100 is not.

Why Do We Need Leap Years?

Earth completes one orbit around the Sun in approximately 365.2422 days (a tropical year). The Gregorian calendar, introduced by Pope Gregory XIII in 1582, uses leap years to approximate this fractional day:

• Every 4 years: adds 0.25 days/year → 365.25 (slightly too many)
• Skip century years: subtracts 0.01 days/year → 365.24 (slightly too few)
• Keep 400-year centuries: adds back 0.0025 days/year → 365.2425 (very close to 365.2422)

This system is accurate to within 1 day every 3,236 years.

How to Use This Tool

1. Check a Single Year — Enter any year to see if it is a leap year, with a visual breakdown of each divisibility rule, a 20-year calendar grid, century statistics, and interesting facts.
2. Find Leap Years in Range — Enter a start and end year (up to 2000 years apart) to get a complete list of all leap years in that period, with a count and percentage.
3. Find Next / Previous Leap Year — Enter any year to discover the nearest leap years before and after it, along with the distance in years.

Frequently Asked Questions

What is a leap year?

A leap year is a year with 366 days instead of the usual 365. The extra day is added to February, making it 29 days long. Leap years occur roughly every 4 years to keep our calendar aligned with Earth's orbital period around the Sun, which takes approximately 365.2422 days.

How do you determine if a year is a leap year?

A year is a leap year if: (1) it is divisible by 4, AND (2) if it is a century year (divisible by 100), it must ALSO be divisible by 400. For example, 2024 is a leap year (divisible by 4, not a century year). 1900 is NOT a leap year (divisible by 100 but not 400). 2000 IS a leap year (divisible by 400).

Why is the year 2000 a leap year but 1900 is not?

Both are century years divisible by 100. The Gregorian calendar has a special rule: century years are only leap years if also divisible by 400. Since 2000 / 400 = 5, 2000 is a leap year. But 1900 / 400 = 4.75, so 1900 is not.

What are the next leap years?

The next upcoming leap years are 2028, 2032, 2036, 2040, 2044, 2048, 2052, 2056, 2060, 2064, 2068, 2072, 2076, 2080, 2084, 2088, 2092, and 2096. Note that 2100 will NOT be a leap year.

How many leap years are in a century?

Most centuries have 24 leap years. Centuries that end with a year divisible by 400 have 25 leap years. The 20th century (1901–2000) had 25, while the 21st century (2001–2100) will have 24.

Why do we need leap years?

Earth takes approximately 365.2422 days to orbit the Sun. Without leap years, the calendar would drift by about 1 day every 4 years, or about 24 days per century. Leap years keep our calendar synchronized with Earth's orbital position so that seasons stay aligned with calendar months.

Additional Resources

• Leap year - Wikipedia
• Gregorian calendar - Wikipedia