What Is a Leap Year Calculator?
A Leap Year Calculator checks whether a particular year has
365 or 366 days. In a leap year, February contains 29 days
instead of the usual 28.
The extra day helps keep the calendar aligned more closely
with Earth's orbit around the Sun. Leap years normally occur
every four years, but century years follow an additional rule.
Quick Example:
2028 is divisible by 4 and is not a century year.
Therefore, 2028 is a leap year and February
2028 has 29 days.
How to Calculate a Leap Year
The Gregorian leap-year rule is based on whether the year
is divisible by 4, 100, and 400.
Rule 1: Divisible by 4
A year that is not divisible by 4 is normally not a leap
year. For example, 2026 is not divisible by 4, so it is a
common year.
Rule 2: Century Years
If a year is divisible by 100, being divisible by 4 is not
enough. A century year must also be divisible by 400 to be
a leap year.
Rule 3: Divisible by 400
A century year divisible by 400 is a leap year. This is why
2000 was a leap year, while 1900 and 2100 are not.
How Many Days Are in a Leap Year?
A leap year contains 366 days. A common
year contains 365 days.
The difference comes entirely from February. February has
29 days during a leap year and 28 days during a common year.
Common Year: 365 days
Leap Year: 366 days
Common February: 28 days
Leap-Year February: 29 days
Why Do We Have Leap Years?
A calendar year of exactly 365 days does not perfectly match
the length of the Earth's orbit around the Sun. The calendar
therefore needs occasional adjustment.
Adding an extra day in certain years helps keep calendar
dates and seasons from gradually drifting apart. The
Gregorian rules also skip some century leap years to make
the calendar more accurate over long periods.
Why Is 2000 a Leap Year but 2100 Is Not?
Both years are divisible by 100, so the century-year rule
applies. A century year must be divisible by 400 to qualify
as a leap year.
2000 ÷ 400 = 5
2000 is divisible by 400, so it is a leap year.
2100 ÷ 400 = 5.25
2100 is not divisible by 400, so it is not a leap year.
Frequently Asked Questions
What is a leap year?
A leap year is a calendar year containing 366 days instead
of 365. The additional day is February 29.
How can I tell if a year is a leap year?
A year is a leap year if it is divisible by 4, except
century years must also be divisible by 400.
Is every fourth year a leap year?
Usually, but not always. Century years such as 1900 and
2100 are excluded unless they are divisible by 400.
Was 2000 a leap year?
Yes. The year 2000 is divisible by 400, so it qualifies as
a leap year under the Gregorian calendar rules.
Is 2100 a leap year?
No. Although 2100 is divisible by 4 and 100, it is not
divisible by 400.
How many days are in February during a leap year?
February contains 29 days in a leap year instead of its
usual 28 days.
How many days are in a leap year?
A leap year contains 366 days, which is one day more than
a common year.
How often do leap years occur?
They generally occur every four years, with exceptions for
century years that are not divisible by 400.