Leap Year Checker: Is It a Leap Year and Why

What is it?

The Leap Year Checker tells you if a year is a leap year, explains why, and lists the nearest leap years.

Who is it for?

Students learning calendar rules, programmers checking date code, and people born on 29 February.

How to use it

1. Type a year, such as 2028.
2. Read whether it is a leap year and why.
3. See the nearest leap years before and after.

The rules

1. A year divisible by 4 is a leap year (2028),
2. except years divisible by 100, which are not (1900, 2100),
3. except years divisible by 400, which are (2000, 2400).

Why we have leap years

The Earth takes about 365.2422 days to go round the Sun. Adding a day almost every four years keeps seasons and festivals on the same dates over centuries.

Good to know

• A leap year has 366 days; 29 February is the extra day.
• People born on 29 February usually celebrate on 28 February or 1 March in other years.
• Leap years affect interest calculations: some banks count 366 days in a leap year.

Worked examples

• 2028: divisible by 4, not by 100 → leap year.
• 1900: divisible by 100 but not by 400 → not a leap year, even though it is divisible by 4.
• 2000: divisible by 400 → leap year. That’s why 2000 had a 29 February but 1900 didn’t.
• 2100: will not be a leap year.

Why the 100 and 400 rules?

Adding a day every 4 years gives an average year of 365.25 days, slightly too long. Skipping three leap days every 400 years brings the average to 365.2425 days, very close to the real 365.2422. Without these rules, seasons would slowly drift.

Leap years in spreadsheets and code

• Excel wrongly treats 1900 as a leap year (an old compatibility bug), so dates before March 1900 can be off by a day.
• In code, check with: divisible by 4 and (not divisible by 100 or divisible by 400).

Related tools

Days Between Dates · Age Calculator

Errors and how to fix them

• Negative or year 0: historical years before the calendar existed aren’t meaningful; use years from 1583 on for Gregorian rules.

Open the tool: Leap Year Checker

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