Leap Years Explained: Rules, Examples & Dates
A leap year adds one extra day to February, giving the year 366 days instead of 365. Learn why leap years are needed, how the Gregorian calendar rules work, and how to check whether a year is a leap year with our Leap Year Calculator.
What Is a Leap Year?
A leap year is a calendar year with an extra day added to February. A normal year has 365 days, while a leap year has 366 days. The additional day is February 29, known as Leap Day.
Leap years help keep the calendar aligned with Earth's seasonal cycle over long periods of time.
Why Do We Need Leap Years?
Earth takes approximately 365.2422 days to complete one cycle relative to the seasons. Because a calendar year normally contains 365 days, the difference would gradually shift the calendar away from the seasonal cycle.
Adding an extra day at appropriate intervals helps keep the calendar synchronized with the seasonal year. The Gregorian calendar uses a specific set of rules to make this adjustment more precise.
How to Calculate a Leap Year
Under the Gregorian calendar, a year is a leap year when it follows these rules:
Divisible by 4
The year must be evenly divisible by 4.
Century Exception
If the year is divisible by 100, it is normally not a leap year.
Divisible by 400
A century year is a leap year when it is also divisible by 400.
Example: 1900 vs. 2000
Year 1900:
- • Divisible by 4? Yes.
- • Divisible by 100? Yes.
- • Divisible by 400? No.
- Result: Not a Leap Year
Year 2000:
- • Divisible by 4? Yes.
- • Divisible by 100? Yes.
- • Divisible by 400? Yes.
- Result: Leap Year
How the Leap Year Calculator Works
01. Enter a Year
Enter the year you want to check and the calculator evaluates it using the standard Gregorian calendar rules.
02. Get the Result
The calculator identifies whether the selected year is a leap year or a common year.
03. Check the Rules
Review the calculation rules to understand why the selected year is classified as a leap year or not.
04. Explore Nearby Years
Use the results to identify nearby past and future leap years for planning and reference.
Leap Year FAQs
Is 2024 a leap year?
Yes. 2024 is divisible by 4 and is not divisible by 100, so it is a leap year with 366 days.
When is the next leap year?
The next leap years after 2024 include 2028, 2032, 2036, and 2040.
How often does a leap year occur?
Most leap years occur every four years, but century years follow the additional 100 and 400 divisibility rules.
Check Any Year Quickly
Use the AptCalc Leap Year Calculator to quickly check whether a year is a leap year and understand the calendar rules behind the result.