# Free online leap year calculator

> A leap year has 366 days instead of 365. This calculator applies the Gregorian rule — divisible by 4, except centuries, except multiples of 400.

Check whether any year is a leap year and find the next and previous leap years using the Gregorian calendar rules.

**Interactive version:** https://onlinecalculator.me/math/leap-year/
**Category:** Math

## How to use

1. Enter any year in the input field.
2. Click **Check Year**.
3. See whether the year is a leap year, how many days it has, and the nearest leap years before and after it.
4. Use **Share with my numbers** to copy a link with the year pre-filled.

## How it works

The Gregorian calendar leap year rules in priority order:

| Condition | Result |
|-----------|--------|
| Year divisible by 400 | Leap year |
| Year divisible by 100 | Not a leap year |
| Year divisible by 4 | Leap year |
| Otherwise | Not a leap year |

## Worked example

**Is 2100 a leap year?**

- 2100 ÷ 4 = 525 → divisible by 4 ✓
- 2100 ÷ 100 = 21 → divisible by 100 ✗ (overrides the 4 rule)
- 2100 ÷ 400 = 5.25 → not divisible by 400

Result: **2100 is not a leap year** (365 days).

**Is 2000 a leap year?**

- 2000 ÷ 4 = 500 ✓
- 2000 ÷ 100 = 20 ✓ (century — would normally fail)
- 2000 ÷ 400 = 5 ✓ (overrides the century rule)

Result: **2000 is a leap year** (366 days).

## Frequently asked questions

### What makes a year a leap year?

Three rules apply in order. A year is a leap year if it is divisible by 4 — unless it is also divisible by 100, in which case it is not a leap year — unless it is also divisible by 400, in which case it is a leap year again. So 2000 was a leap year, 1900 was not.

### Why do we have leap years?

The solar year is approximately 365.2422 days long. Without correction, the calendar would drift about one day every four years, shifting seasons over time. Adding a leap day roughly every four years keeps the calendar aligned with Earth's orbit.

### How many leap years are there in a century?

Most centuries have 24 leap years (skipping the century year). A century that is also a multiple of 400 — like 1600, 2000, 2400 — has 25 leap years because the century year itself qualifies.

### What happens to people born on February 29?

They celebrate their birthday on February 28 or March 1 in non-leap years, depending on personal preference and local law. Some countries have specific rules for official purposes.

### Is the Gregorian calendar perfect?

No. The Gregorian calendar overestimates the solar year by about 26 seconds per year, accumulating roughly one day of error every 3,300 years. This is considered acceptable for practical purposes.

## Sources

- [Leap year](https://en.wikipedia.org/wiki/Leap_year) — Wikipedia
- [Leap Years](https://aa.usno.navy.mil/faq/leap_years) — U.S. Naval Observatory

## Related calculators

- [Prime factorization calculator](https://onlinecalculator.me/math/prime-factorization/) — Find all prime factors of a number.
- [Age calculator](https://onlinecalculator.me/date-time/age/) — Calculate exact age between two dates.
- [Days between dates](https://onlinecalculator.me/date-time/date-difference/) — Count the days between any two calendar dates.
- [Week number calculator](https://onlinecalculator.me/date-time/week-number/) — Find the ISO or US week number for any date.

---

Part of [onlinecalculator.me](https://onlinecalculator.me/) — free calculators that run entirely in your browser.
Machine-readable index: https://onlinecalculator.me/llms.txt