MORE INFORMATION
The date system used by Excel is based on the Gregorian
calendar, first established in 1582 by Pope Gregory XIII. This calendar was
designed to correct the errors introduced by the less accurate Julian calendar.
In the Gregorian calendar, a normal year consists of 365 days.
Because the actual length of a sidereal year (the time required for the Earth
to revolve once about the Sun) is actually 365.25635 days, a "leap year" of 366
days is used once every four years to eliminate the error caused by three
normal (but short) years. Any year that is evenly divisible by 4 is a leap
year: for example, 1988, 1992, and 1996 are leap years.
However,
there is still a small error that must be accounted for. To eliminate this
error, the Gregorian calendar stipulates that a year that is evenly divisible
by 100 (for example, 1900) is a leap year only if it is also evenly divisible
by 400.
For this reason, the following years ARE NOT leap years
1700, 1800, 1900, 2100, 2200, 2300, 2500, 2600
because they are evenly divisible by 100 but NOT by 400.
The following years ARE leap years
because they are evenly divisible by both 100 and 400.
Because versions of Microsoft Excel earlier than Excel 97 handle only years
from 1900 to 2078, only the year 1900 is subject to the 100/400 exclusion rule
of leap years in Microsoft Excel. However, in order to be compatible with other
programs, Microsoft Excel treats the year 1900 as a leap year.
For
additional information, please see the following article in the Microsoft
Knowledge Base:
214058
XL2000: Days of the Week Before March 1, 1900 Are Incorrect
To Determine If a Year Is a Leap Year
To determine if a year is a leap year, follow these steps:
- If the year is evenly divisible by 4, go to step 2.
Otherwise, go to step 5.
- If the year is evenly divisible by 100, go to step 3.
Otherwise, go to step 4.
- If the year is evenly divisible by 400, go to step 4.
Otherwise, go to step 5.
- The year is a leap year (it has 366 days).
- The year is not a leap year (it has 365 days).
Formula to Determine If a Year Is a Leap Year
The following formula will determine whether the year number
entered into a cell (in this example, cell A1) is a leap year:
=IF(OR(MOD(A1,400)=0,AND(MOD(A1,4)=0,MOD(A1,100)<>0)),"Leap Year",
"NOT a Leap Year")
If the value in cell A1 is this The formula returns
----------------------------------------------------------
1992 Leap Year
2000 Leap Year
1900 NOT a Leap Year