Understanding How Excel Stores Dates and Time:-


On a Windows PC, Excel stores dates as the number of days since January 1, 1900. For a date such as 9/15/2007, Excel actually stores the value 39,340, but it formats the date to show you a value such as 09/15/2007.

On a Mac running Mac OS, Excel stores the dates as the number of days since January 1, 1904. The original designers of the Mac OS were trying to squeeze the OS into 64K of ROM. Since every byte mattered, it seemed unnecessary to add a couple lines of code to handle the fact that 1900 is not a leap year. Excel for the Mac adopted the 1904 convention.

Excel for Windows, which needed to be compatible with Lotus 1-2-3, adopted the 1900 convention. Excel provides a complete complement of functions to deal with dates, including functions that convert data from text to dates and back. Excel stores times as decimal fractions of days. For example, you can enter noon today as =TODAY() + 0.5. You can enter 9 a.m. as =TODAY() + 0.375. Again, the number format handles converting the decimals to the appropriate display.