About the Leap Year Calculator
Enter a year and the calculator tells you at once whether it is a leap year and, more usefully, why. It shows how many days the year has, how many days February has, and the previous and next leap years. A second mode lists every leap year between two years, up to a span of 500 years. The Gregorian rule is used for every year from 1 to 9999, including years before the calendar was adopted in 1582, so the results for early years follow the modern rule and not the Julian calendar that was used at the time. Everything is worked out in your browser.
Updated October 2026
How to use the Leap Year Calculator
- 1For one year, type it in the Year box (1 to 9999).
- 2Read whether it is a leap year, the reason, the days in the year and in February, and the neighbouring leap years.
- 3For a list, switch to Year range and enter a start and an end year.
- 4Copy the list of leap years if you need it elsewhere.
Why we have leap years
The Earth takes about 365.2422 days to go once round the sun. A calendar of exactly 365 days drifts ahead by nearly a quarter of a day each year, so after a century the seasons would arrive about 24 days late. Adding a leap day every four years fixes most of the drift, but it overcorrects slightly, so the Gregorian calendar leaves out three leap days every 400 years. The rules in this calculator are exactly that arrangement, and it keeps the calendar within about a day of the seasons for roughly three thousand years.
A quick way to check by hand
- If the year is not divisible by 4, it is not a leap year.
- If it is divisible by 4 but not by 100, it is a leap year (2024, 2028).
- If it is divisible by 100 but not by 400, it is not a leap year (1900, 2100).
- If it is divisible by 400, it is a leap year (2000, 2400).
- February then has 29 days in a leap year and 28 days in other years.
Where leap years matter
Leap years affect age and date calculations, interest on loans counted by the day, payroll and rental periods, software that stores dates and anyone born on 29 February. Counting the leap days in a range tells you how many extra days a period contains. A person born on 29 February has a real birthday only in leap years, and many places treat 28 February or 1 March as the birthday in other years.
Related tools
The Date Calculator adds or subtracts days from a date, the Age Calculator gives exact ages in years, months and days, the Days Between Dates calculator counts the days between two dates, the Day of the Week Calculator tells you which weekday a date falls on and the Calendar Maker prints a calendar for any year.
Features
- Gregorian rule: every 4 years, except centuries not divisible by 400
- Plain-English reason for each result
- Days in the year and days in February
- Previous and next leap year
- Leap years in any range up to 500 years
- Years 1 to 9999
- Runs in your browser
Frequently asked questions
What makes a year a leap year?
In the Gregorian calendar 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. So 2024 is a leap year, 1900 and 2100 are not, and 2000 was.
Why was 1900 not a leap year?
1900 is divisible by 100 but not by 400, so it is skipped. The rule exists because a year is a little shorter than 365.25 days, so adding a day every four years would slowly push the calendar ahead of the seasons.
How many leap years are there in 400 years?
There are 97. A leap day every four years would give 100 in 400 years, but three of the century years (such as 1700, 1800 and 1900) are skipped, leaving 97. That makes the average year 365.2425 days long.
What is the next leap year after 2096?
It is 2104. The year 2100 is divisible by 100 but not by 400, so it is not a leap year, and the calendar skips from 2096 to 2104.
Does the calculator work for years before 1582?
It applies the Gregorian rule to every year, which is called the proleptic Gregorian calendar. Before 1582 most of Europe used the Julian calendar, in which every fourth year was a leap year with no exceptions, so historical dates of that era follow a different rule.
Why is the range limited to 500 years?
Five hundred years covers all the rules and keeps the list short enough to read and copy. If you need a longer span, check it in several pieces, or count: there is one leap year every four years, minus three every four centuries.