Why isn’t 1900 a leap year?

Years divisible by 100 are skipped unless they are also divisible by 400. 1900 is divisible by 100 but not by 400, so it is not a leap year. 2000 is divisible by both, so it is.

Does the tool work for years before 1583?

It will compute a result, but historically those years used the Julian calendar in most of Europe. The Gregorian rule was introduced in 1582; results before that are mathematically correct but not what those societies actually observed.

How big a range can I scan?

Up to 500 years. The cap keeps the page responsive — the loop runs synchronously, so very large ranges would block input briefly.

What is an "exceptional" leap year?

A common informal name for century years that are leap years (1600, 2000, 2400, …). Most century years are skipped under the divisible-by-400 exception.

Does the rule apply to the Julian calendar?

No. The Julian calendar treats every year divisible by 4 as a leap year, with no century exception. This tool always uses the Gregorian rule.

Leap Year Calculator

Check if a year is a leap year using the Gregorian rule, with next/previous leap years and range scan.

Written by Golam Rabbani, Founder & Lead Engineer

This interactive tool requires JavaScript. Read the formula and worked example below; you can compute the result by hand.

How to use this leap year calculator

Enter the year you want to check (1 to 9999).
Optionally enter a range end year (up to 500 years span) to list every leap year in the window.
Press "Check leap year".
Read the answer plus the previous and next leap years.
Use Reset to start over or Copy to paste the explanation elsewhere.

About this leap year calculator

A leap year on the Gregorian calendar is a year with 366 days instead of 365: an extra day (29 February) is added so the calendar stays aligned with the solar year. The rule has three steps: a year is a leap year if it is divisible by 4, except if it is divisible by 100, unless it is also divisible by 400. That is why 1900 was not a leap year but 2000 was.

This tool runs the rule directly on the year you enter, then walks backwards and forwards from that year to find the closest leap years on either side. If you also give a range end, it loops through every year in the inclusive range and lists those that pass the test, capped at 500 years to keep the page fast.

Worked example: enter 2024 and leave the range blank. The tool reports "2024 is a leap year — divisible by 4 and not by 100", with previous leap year 2020 and next leap year 2028. Now enter 2024 with range end 2050 and the tool lists 2024, 2028, 2032, 2036, 2040, 2044, 2048 — every leap year in that span.

Use it to plan birthdays for people born on 29 February, double-check date arithmetic, or settle a quick "is this a leap year?" question.

FAQ

Why isn’t 1900 a leap year?: Years divisible by 100 are skipped unless they are also divisible by 400. 1900 is divisible by 100 but not by 400, so it is not a leap year. 2000 is divisible by both, so it is.
Does the tool work for years before 1583?: It will compute a result, but historically those years used the Julian calendar in most of Europe. The Gregorian rule was introduced in 1582; results before that are mathematically correct but not what those societies actually observed.
How big a range can I scan?: Up to 500 years. The cap keeps the page responsive — the loop runs synchronously, so very large ranges would block input briefly.
What is an "exceptional" leap year?: A common informal name for century years that are leap years (1600, 2000, 2400, …). Most century years are skipped under the divisible-by-400 exception.
Does the rule apply to the Julian calendar?: No. The Julian calendar treats every year divisible by 4 as a leap year, with no century exception. This tool always uses the Gregorian rule.