Use this leap year calculator to check whether any year has 365 or 366 days, understand why 2000 was a leap year but 2100 will not be.
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Leap year calculator for the 4, 100, and 400 rule Check whether any year is a leap year, see why 2000 was a leap year but 2100 will not be, and review the nearest leap years plus key century-year examples.
Quick presets
Enter a valid year Provide a whole-number year between 1 and 9999.
Leap year calculator guide: 2000 versus 2100, Gregorian rules, and next leap years
A leap year calculator tells you whether any year is a leap year or a common year, explains which Gregorian rule applies, and shows the nearest past and future leap years. The biggest search intent here is rarely just a yes-or-no answer. Users usually want to know why 2000 was a leap year, why 1900 and 2100 are not, what the next leap year is, and why leap years exist in the first place.
The Gregorian leap-year rule explained
A year is a leap year if it is divisible by 4, except for century years divisible by 100, which must also be divisible by 400. This means most years divisible by 4 gain an extra day, but century years need one extra check before they qualify.
That rule is why 2024 is a leap year, 2023 is not, 1900 was not, 2000 was, and 2100 will not be. Without the century correction, the calendar would drift away from the solar year over time.
Leap year = (year mod 400 = 0) OR (year mod 4 = 0 AND year mod 100 ≠ 0)
This is the standard Gregorian leap-year rule used in programming and calendar references.
Why 2000 was a leap year but 1900 and 2100 are not
Century years cause most of the confusion. Years such as 1700, 1800, 1900, 2100, 2200, and 2300 are all divisible by 4, but that is not enough. Because they are also divisible by 100, they only remain leap years if they are divisible by 400.
The year 2000 passed that final test, so it was a leap year. The year 1900 did not, so it stayed a common year. The same logic makes 2100, 2200, and 2300 common years, while 2400 will be a leap year.
Why leap years exist at all
A solar year is not exactly 365 days long. It is about 365.2422 days, so a calendar with no correction would slowly drift against the seasons. Adding one extra day every four years gets close, but not close enough over the long term.
The century exception improves the average calendar year to 365.2425 days, which tracks the solar year much more closely. That is why leap years are a rule-based correction rather than a simple every-four-years pattern with no exceptions.
How to read the calculator result
The headline answer tells you whether the selected year is a leap year or a common year, but the supporting rows are just as useful. The day count shows whether the year has 365 or 366 days, the next and previous leap years show the rhythm around the selected year, and the century checkpoints make the 1900/2000/2100 pattern obvious at a glance.
That extra context matters when the question is not only “is this a leap year?” but “why does this year behave differently from the one before it?” A year such as 2024 sits on the ordinary 4-year rhythm, while 2100 breaks the pattern because century years need the extra 400-rule check.
Worked example: checking 2100
Start with the quick test: 2100 is divisible by 4, so it looks like it could be a leap year. Then apply the century-year rule. Because 2100 is divisible by 100, it must also be divisible by 400 to remain a leap year.
It is not divisible by 400, so 2100 is a common year with 365 days. That single example explains why a leap year calculator is more useful than the oversimplified rule many people remember from school.
Leap-year birthdays and real-world use
People born on 29 February often celebrate on 28 February or 1 March in non-leap years depending on preference, tradition, or local legal rules. That is why leap year birthday calculator and leap year age calculator searches often sit beside the broader leap year calculator query.
Software developers, spreadsheet users, historians, teachers, and students also use leap-year checks when debugging date arithmetic, validating calendars, or explaining why the number of days in a year changes.
Leap-year cadence and planning
The nearest leap years are useful because they show the cadence around the selected year. In most cases the answer sits four years away in either direction, but century years are where the spacing can look unusual. That is why this calculator surfaces both the previous and next leap years instead of stopping at the headline yes-or-no answer.
If you are planning birthdays, calendar logic in software, or long-range scheduling, the cadence view helps you compare the selected year with the year before it, the year after it, and the century checkpoints that can interrupt the ordinary 4-year rhythm. The 1900/2000/2100/2400 examples are the fastest way to remember the rule in practice.
Limits of this calculator and nearby tools
This page answers whether a year is a leap year and explains the rule behind that answer. It does not calculate an age from a birth date, estimate a due date, or resolve country-specific legal treatment of 29 February birthdays.
If the practical task is age or elapsed time, use an age calculator or date difference calculator. If the question is how many days remain until an event, a countdown calculator is the better match.
Frequently asked questions
Is 2100 a leap year?
No. The year 2100 is divisible by 100 but not by 400, so the century exception makes it a common year with 365 days.
Why was 2000 a leap year but 1900 was not?
Both years are divisible by 100, so they trigger the century-year exception. The difference is that 2000 is also divisible by 400, so it stays a leap year, while 1900 is not divisible by 400 and therefore stays a common year.
What is the next leap year?
The next leap year is whichever upcoming year satisfies the 4, 100, and 400 rule. In the ordinary four-year rhythm this is often just four years after the last leap year, but century years can interrupt that pattern.
Why do leap years exist?
Leap years exist because the solar year is slightly longer than 365 days. Adding an extra day in selected years keeps the calendar aligned with the seasons instead of letting it drift over time.
How do you tell if a year is a leap year?
Check whether the year is divisible by 400 first. If not, check whether it is divisible by 100. If it is divisible by 100 but not by 400, it is not a leap year. Otherwise, if it is divisible by 4, it is a leap year.
Is 1900 a leap year?
No. The year 1900 is divisible by 100 but not by 400, so it is a common year under the Gregorian rule.
Will 2400 be a leap year?
Yes. The year 2400 is divisible by 400, so it remains a leap year even though it is also a century year.
What happens to birthdays on 29 February in non-leap years?
People born on 29 February usually celebrate on either 28 February or 1 March in non-leap years. The exact legal treatment can vary by country and context.
Is every year divisible by 4 a leap year?
No. That shortcut works for many years, but it fails for century years such as 1900 and 2100. Those years must also be divisible by 400 to count as leap years.
What is the difference between a leap year calculator and a leap year age calculator?
A leap year calculator tells you whether a year has 365 or 366 days and why. A leap year age calculator is a more specialized age tool that uses a birth date and a comparison date, often with extra handling for 29 February birthdays.
How many days are in a leap year?
A leap year has 366 days. The extra day is February 29, which keeps the calendar aligned with the solar year.
Why does the calculator show century checkpoints like 1900, 2000, 2100, and 2400?
Those examples make the century rule easy to remember. 1900 and 2100 are common years because they are divisible by 100 but not 400, 2000 stays a leap year because it is divisible by 400, and 2400 also stays a leap year for the same reason.
How far away is the next leap year?
The calculator shows both the previous and next leap year so you can see the cadence around the selected year. Most years are four years from the next leap year, but century-year exceptions can change that spacing.
