functions

Leap Year Calculator | Determine If a Year Is a Leap Year

What the Leap Calculator does

Behind the inputs above sits one rule: Leap year if divisible by 4, except centuries not divisible by 400. The tool evaluates it instantly with the values you enter.

Scroll past the calculator for a quick-reference table, a step-by-step methodology with a fully worked example, and answers to the questions people most often ask about leap year calculator.

Quick reference

Year	Leap?	Reason
2024	Yes	Divisible by 4
1900	No	Century, not ÷400
2000	Yes	Century ÷ 400
2026	No	Not divisible by 4

info Leap Calculator

Free math calculator — enter your numbers and get an instant, accurate result.

info Private by design

Everything runs locally in your browser. No uploads, no accounts, no tracking.

info Works everywhere

Fully responsive and mobile-friendly — calculate on any device, any time.

info Educational

Includes the formula and step-by-step explanation so you understand the math, not just the answer.

Interpretation guide

Result	Meaning
Leap year	366 days, February has 29
Common year	365 days, February has 28
Next leap year	Upcoming year with Feb 29

lightbulb Worked example: is 2100 a leap year?

A developer testing date logic checks the century edge case 2100. Step 1: 2100 ÷ 4 = 525 — passes the divisible-by-4 rule. Step 2: 2100 ÷ 100 = 21 — it is a century year, so it must also pass the divisible-by-400 rule. Step 3: 2100 ÷ 400 = 5.25 — not a whole number, so it fails.

Result: 2100 is not a leap year — 365 days, February has 28 days.

What this means: Century years skip the leap day unless divisible by 400, which is why 2000 was a leap year but 1900 and 2100 are not. Date code that only checks divisibility by 4 gets this wrong — the century rule is the classic leap-year test case, and the next century leap year after 2000 is 2400.

Formula & methodology

Formula: Leap year if divisible by 4, except centuries not divisible by 400

How leap years are determined

The Gregorian calendar applies three rules in order:

Divisible by 4 → leap year (e.g. 2028).
…unless it is a century year (divisible by 100) → common year (e.g. 2100).
…unless the century year is also divisible by 400 → leap year (e.g. 2000).

Why the exceptions exist

Earth's orbit takes about 365.2422 days. Adding a day every four years overshoots slightly, so skipping the leap day in three out of four century years trims the average calendar year to 365.2425 days — drifting just one day every ~3,300 years. Leap years have 366 days, with February 29 as the extra day.

Authoritative source: Wolfram MathWorld

Frequently asked questions

How do I know if a year is a leap year?

Enter the required values into the input fields and press the calculate button. The tool applies the formula Leap year if divisible by 4, except centuries not divisible by 400 and returns the result with a short explanation of each step, so you can check the working yourself.

Is 2026 a leap year?

The Leap Calculator is free, private, and accurate: it runs entirely in your browser (no uploads, no accounts), applies the standard calculation, and explains each step so you can verify the result. Calculates leap year using Leap year if divisible by 4, except centuries not divisible by 400, live in your browser. There is no limit on usage, and it works on any device.

Why are some century years not leap years?

The Gregorian calendar's rule — leap if divisible by 4, except centuries unless divisible by 400 — corrects for the fact that a solar year is 365.2422 days, not exactly 365.25. Adding a day every 4 years overshoots slightly, so century years skip the leap day, and every 4th century (2000, 2400) restores it. This keeps the calendar aligned with the seasons over millennia.

How many days are in a leap year?

366 — one more than a common year's 365, with the extra day added to February as February 29. That extra day shifts every date's weekday by two positions instead of one after the leap day. A leap year occurs about every four years, which averages out to a year length of 365.2425 days under the Gregorian rule.

Why is the year 2100 not a leap year?

2100 is divisible by 4 (2100 ÷ 4 = 525), but it is a century year, and century years must also be divisible by 400. Since 2100 ÷ 400 = 5.25, 2100 is a common year with 28 days in February. The same rule made 1900 a common year while 2000 stayed leap.

How do programmers test leap-year logic?

They check the tricky boundaries: a normal leap year like 2028, a non-leap year like 2026, a century non-leap year like 2100, and a century leap year like 2000. Getting 1900 and 2100 right while keeping 2000 leap is the classic correctness test for date libraries. This calculator applies the same three-rule check.

Why do we need leap years at all?

Earth's orbit takes about 365.2422 days, not exactly 365. Without the extra day every four years, the calendar would drift roughly 24 days per century and the seasons would slide through the months. The century exception trims the average calendar year to 365.2425 days — close enough that the error is only one day per ~3,300 years.

What weekday do leap days fall on?

February 29, 2024 was a Thursday; the next, February 29, 2028, is a Tuesday. Because a leap year has 366 days (52 weeks plus 2 days), leap days shift forward two weekdays each cycle, except across century boundaries. People born on February 29 — called ‘leaplings’ — celebrate on February 28 or March 1 in common years.

Do all countries use the same leap-year rule?

All countries using the Gregorian calendar do — the divisible-by-4, except-centuries, except-multiples-of-400 rule is universal there. A few other calendars differ: the Hebrew calendar adds a whole leap month 7 times in 19 years, and the Islamic tabular calendar adds a day 11 times in 30 years. This calculator follows the Gregorian rule.

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