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Leap Year Checker

Gregorian leap tests plus upcoming leap year hints.

About Leap Year Checker

The Gregorian calendar adds an extra day — February 29 — to approximately every fourth year to keep the calendar aligned with the Earth's roughly 365.25-day orbit around the sun. But the rule is more nuanced than simply 'every four years'. Century years (years divisible by 100) are skipped unless they are also divisible by 400, which is why 1900 was not a leap year while 2000 was. This three-part rule — divisible by 4, except by 100, except by 400 — is what the Gregorian calendar uses to stay within 26 seconds of the true solar year over centuries. This leap year checker makes the determination instant for any individual year or range of years. Enter a single year and the tool tells you whether it is a leap year, which specific rule applied, and whether February has 28 or 29 days.

Why use Leap Year Checker

Instant Yes/No with Rule Explanation

The tool does not just output a boolean — it shows which of the three Gregorian divisibility rules determined the answer. You see exactly why 2100 is not a leap year (divisible by 100 but not by 400) rather than just being told it is not.

Range Mode for Span Scanning

List every leap year between any two years in one view. This is useful for birthday planners dealing with February 29 dates, for developers testing date-edge-case scenarios, or for educators preparing examples spanning multiple decades.

Rule Transparency

The three-rule Gregorian algorithm is displayed step by step for the entered year. Each divisibility check is shown with its result, making the tool educational as well as functional.

February Day Count

The tool explicitly states whether February has 28 or 29 days for the checked year. This is the most directly actionable output for scheduling, form validation, or date-picker boundary checks.

Past and Future Coverage

The checker works across the full Gregorian calendar range — past historical dates, the present, and centuries into the future. Whether you need to verify 1582 (the Gregorian reform year) or 2400, the same rules apply.

Offline, Instant Results

Leap year calculation is pure arithmetic that runs entirely in the browser without any server request. Results are available offline, appear without delay, and require no account or data submission.

How to use Leap Year Checker

Choose a mode: Single Year to check one year, or Year Range to list all leap years in a span
For Single Year: type the year into the input field and read the immediate yes/no result
Review which of the three Gregorian rules — divisible by 4, divisible by 100, or divisible by 400 — determined the outcome
Check the February day count shown below the result: 28 or 29 days
For Year Range: enter a start year and end year to generate a complete list of all leap years in that span
Copy the result or the list for use in scheduling, development work, or educational reference

When to use Leap Year Checker

When a person born on February 29 needs to know which years they have an actual birthday
When a developer writing date-handling code needs to verify boundary conditions around February 28–29
When a scheduler needs to confirm whether a February 29 event date is valid in a specific upcoming year
When a student is learning the Gregorian calendar rules and wants an interactive explanation of each case
When planning a multi-year event calendar and needing to identify all years with a February 29
When verifying that legacy data containing year values handles the divisible-by-100 century exception correctly

Examples

Standard leap year

Input: Year: 2024

Output: Leap year: YES (divisible by 4, not by 100) · February: 29 days

Century non-leap year

Input: Year: 1900

Output: Leap year: NO (divisible by 100, not by 400) · February: 28 days

Century leap year

Input: Year: 2000

Output: Leap year: YES (divisible by 400) · February: 29 days

Tips

The full Gregorian rule in one sentence: divisible by 4 is a leap year, except divisible by 100 is not, except divisible by 400 is
Year 2100 is NOT a leap year — it is divisible by 100 but not by 400, so the century exception applies
People born on February 29 (leaplings) commonly celebrate on February 28 or March 1 in non-leap years
In JavaScript, new Date(year, 1, 29).getMonth() === 1 returns true only in leap years — a quick programmatic check
The Julian calendar had no divisible-by-400 override, causing it to drift about 3 extra days per 400 years relative to the Gregorian calendar

Frequently Asked Questions

What is the leap year rule?▾

A year is a leap year if it is divisible by 4, except that years divisible by 100 are not leap years, unless they are also divisible by 400. In short: divisible by 400 → leap; divisible by 100 but not 400 → not leap; divisible by 4 but not 100 → leap; all others → not leap.

Why was 1900 not a leap year but 2000 was?▾

Both 1900 and 2000 are divisible by 100, which triggers the century exception to the four-year rule. However, 2000 is also divisible by 400, which overrides the century exception and makes it a leap year. 1900 is not divisible by 400, so it remains a non-leap century year.

How often does a leap year occur?▾

Approximately every four years, but with exceptions at century years. In any 400-year Gregorian cycle, there are exactly 97 leap years — giving an average year length of 365.2425 days, very close to the actual tropical year of 365.2422 days.

When was the Gregorian calendar adopted?▾

The Gregorian calendar was introduced by Pope Gregory XIII in October 1582 to correct the accumulated drift of the Julian calendar. Different countries adopted it at different times — Britain and its colonies in 1752, Russia not until 1918.

What happens if you are born on February 29?▾

People born on February 29 are sometimes called leaplings or leap-year babies. In non-leap years they typically celebrate on February 28 or March 1, depending on personal preference and legal jurisdiction. Some countries recognise March 1 as the legal birthday equivalent.

Does every culture use the same leap year rule?▾

No. The Hebrew calendar adds a leap month approximately every three years. The Islamic calendar has no leap-year mechanism and drifts against the solar year. The Ethiopian and Persian calendars use different leap-year rules. The Gregorian leap year rule applies only to the Gregorian (Western civil) calendar.

How does a leap second differ from a leap year?▾

A leap year adds one day (86,400 seconds) to the calendar roughly every four years to account for the solar orbit. A leap second adds exactly one second to UTC on specific occasions to account for the Earth's irregular rotation rate. They correct different astronomical drift sources.

Why do we need leap years at all?▾

Earth takes approximately 365.2422 days to orbit the sun. A 365-day calendar falls behind the solar year by about 6 hours annually. Without leap years, the calendar would drift by roughly one day every four years — seasons would shift noticeably within a few decades.

Explore the category

Glossary

Leap Year: A calendar year containing 366 days rather than 365, with February extended to 29 days. In the Gregorian calendar, leap years occur in years divisible by 4, with exceptions for century years not divisible by 400.
Gregorian Calendar: The internationally used civil calendar introduced by Pope Gregory XIII in 1582. It refined the Julian calendar's leap year rule to keep the calendar year aligned with the tropical (solar) year more accurately.
Julian Calendar: The predecessor to the Gregorian calendar, introduced by Julius Caesar. It adds a leap year every four years without exception, causing it to drift about 11 minutes per year relative to the solar year — roughly one day every 128 years.
Divisible-by-400 Rule: The Gregorian override that makes century years (divisible by 100) into leap years when they are also divisible by 400. Years 1600, 2000, and 2400 are leap years under this rule; 1700, 1800, 1900, and 2100 are not.
Intercalary Day (Feb 29): An extra day inserted into the calendar to keep it synchronised with the solar year. In the Gregorian calendar this day is February 29, added in leap years. The word intercalary means 'inserted between regular days'.
Tropical Year: The time it takes Earth to complete one full orbit around the sun relative to the vernal equinox — approximately 365.2422 days. The Gregorian calendar's average year of 365.2425 days approximates this closely enough that it drifts by only about 26 seconds per year.