Article ID: 214326 - View products that this article applies to.
This article was previously published under Q214326
Microsoft Excel incorrectly assumes that the year 1900 is a leap year. This article explains why the year 1900 is treated as a leap year, and outlines the behaviors that may occur if this specific issue is corrected.
When Lotus 1-2-3 was first released, the program assumed that the year 1900 was a leap year, even though it actually was not a leap year. This made it easier for the program to handle leap years and caused no harm to almost all date calculations in Lotus 1-2-3.
When Microsoft Multiplan and Microsoft Excel were released, they also assumed that 1900 was a leap year. This assumption allowed Microsoft Multiplan and Microsoft Excel to use the same serial date system used by Lotus 1-2-3 and provide greater compatibility with Lotus 1-2-3. Treating 1900 as a leap year also made it easier for users to move worksheets from one program to the other.
Although it is technically possible to correct this behavior so that current versions of Microsoft Excel do not assume that 1900 is a leap year, the disadvantages of doing so outweigh the advantages.
If this behavior were to be corrected, many problems would arise, including the following:
For additional information about this issue, click the article number below to view the article in the Microsoft Knowledge Base:
214058For additional information about determining whether a given year is a leap year, click the article number below to view the article in the Microsoft Knowledge Base:
(http://support.microsoft.com/kb/214058/EN-US/ )XL2000: Days of the Week Before March 1, 1900 Are Incorrect
(http://support.microsoft.com/kb/214019/EN-US/ )XL2000: Method to Determine Whether a Year Is a Leap Year
Article ID: 214326 - Last Review: July 8, 2011 - Revision: 6.0