What is a leap year?

A leap year is a calendar year that contains one extra day February 29, so that the civil calendar stays aligned with Earth’s orbit. Most years have 365 days; a leap year has 366. Adding that extra day every few years prevents the seasons from drifting over long spans of time.

Why this matters: the time Earth takes to complete one orbit around the Sun is not exactly 365 days. The small fractional remainder accumulates and would shift the calendar unless corrected periodically.

The simple rule

You can test a year quickly with two steps:

1. If the year is divisible by 4 → candidate for leap year.
2. If the year is divisible by 100 → only a leap year if it is also divisible by 400.

Put as a condition:

• leap = (year % 4 === 0 && year % 100 !== 0) || (year % 400 === 0)

This yields the familiar behavior: 2000 is a leap year, 1900 is not, 2024 is, and 2100 will not be. The algorithm is short, deterministic, and the one implemented in this calculator.

Quick examples

• 1996 → divisible by 4 and not by 100 → leap.
• 1900 → divisible by 100 but not by 400 → not a leap.
• 2000 → divisible by 400 → leap.
• 2025 → not divisible by 4 → not a leap.

Why those particular divisibility rules?

Because the solar (tropical) year is longer than 365 days by roughly 5 hours, 48 minutes and 45 seconds. If you simply added one day every four years you’d over-correct slightly; the 100 and 400-year checks keep the Gregorian calendar exceptionally accurate over centuries by removing three leap days every 400 years.

What the calculator can do

• Check any single year: type a year and click Check. The tool validates input and shows whether February that year has 28 or 29 days.
• Find leap years in a range: enter start and end years. The calculator lists every leap year in the interval (range limited for performance).
• Show next leap year: the tool computes the next leap year after the current calendar year and can display several upcoming leap years.

This page’s small validation rules (1–9999) and range cap protect browsers from long loops while still covering all practically useful dates.

Edge cases

• Negative, zero or extremely large years: this calculator treats only positive AD years (1–9999) to match typical civil-calendar use. Astronomical year numbering (including year 0 and negative years) follows different conventions and needs special handling.
• People born on Feb 29: legal/administrative handling varies by country. Many celebrate on Feb 28 or Mar 1 in non-leap years; some legal systems specify which date counts for age or contracts.
• Long-range lists: when you request many centuries of years, a server-side approach or an incremental generator is preferable to keep client performance acceptable. Our page limits avoid freezing older browsers.

FAQ

Q1. When is the next leap year?

A: Leap years occur every four years, subject to the 100/400 exceptions. If the current year is not leap, the calculator shows the next one (for reference: leap years after 2024 are 2028, 2032, 2036…).

Q2. How many leap years are there in 100 years?

A: Usually 24 or 25 depending on which century window you inspect, because century years divisible by 100 but not 400 are excluded.

Q3. Do all countries use leap years the same way?

A: The Gregorian calendar (with the 100/400 rules) is the global civil standard for nearly all countries; historical and regional calendars sometimes differ.

Q4. 2026 is a leap year or not?

A: No, 2026 is not a leap year, February 2026 has 28 days.