So, how do you calculate if a year is a leap year? Here is a simple rule: A year is usually a leap year if it is divisible by 4. But if it is divisible by 100, then it is not a leap year unless it is also divisible by 400.
A leap year has 366 days instead of 365 days. In a leap year, February has 29 days instead of 28 days.
The simplest way I have found to remember the rule is "divisible by 4, except for centuries, unless by 400."
Leap Year Rule
Use these three conditions under the Gregorian calendar:
If it is divisible by 400, then it is a leap year.
If it is divisible by 100 but not by 400, it is not a leap year.
If it is divisible by 4, but not 100, it is a leap year.
Otherwise, it is a normal year with 365 days.
For example, the year 2000 was a leap year because 2000 is divisible by 400. However, 1900 was not because it is divisible by 100 but not 400.
The U.S. Naval Observatory describes the same rule for determining leap years in the Gregorian calendar.
Calculation Stepwise
E.g., to check if 2028 is a leap year:
507 times 4 equals 2028.
2028 is perfectly divisible by 4, as 2028 divided by 4 equals 507.
It does not end in a 00 year.
So, 2028 is a leap year.
Now, consider 2100:
2100 is divisible by 4.
It is divisible by 100 too.
But divisible by 400, it is not.
So, 2100 will not be a leap year.
And a handy thing to do with century years is to check divisibility by 400 first. It immediately solves cases like 1600, 2000 and 2400.
Examples:
2024 is a leap year and is divisible by 4.
2025: Not a leap year?
2028: Divisible by 4 - leap year
1900: Not a leap year, divisible by 100 but not 400
2000: leap year (divisible by 400)
2100: Not a leap year.
Why Are There Leap Years?
Earth does not take 365 days to go around the sun. The tropical year is about 365 days, 5 hours, 48 minutes and 46 seconds.
Without any calendar corrections, seasons and calendar dates would progressively become out of sync. The Gregorian leap-year system skips certain leap years in century years, adding extra days to keep the calendar very near to the orbit of the Earth around the Sun.
Common Errors
Avoid these typical errors:
assuming that every year which is divisible by 4 is inevitably a leap year
100-year exemption will be overlooked
Forget the 400-year exception.
Assuming all century years are leap years.
Accounting a leap year as 365 days and not 366
Frequently Asked Questions
1. Will 2026 be a leap year?
2026 is not divisible by 4; hence, it is not a leap year.
2. Will 2028 be a leap year?
Yes. 2028 is divisible by 4 and is not a century year.
3. Days in a leap year?
There are 366 days in a leap year. February has 29 days in a leap year.
Must Read: How Many Weeks are in a Year?
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