This will produce the highest level of accuracy in your date calculations.
For example, in Microsoft Office Excel for Windows, January 1, 1900 is serial number 1, and January 1, 2008 is serial number 39448 because it is 39,448 days after January 1, 1900.
Office Excel stores times as decimal fractions because time is considered a portion of a day. Because dates and times are values, they can be added, subtracted, and included in other calculations.
Originally, Microsoft Excel for the Macintosh was based on the 1904 date system, because it enabled better compatibility with early Macintosh computers that did not support dates before January 2, 1904, and therefore it became the default date system.
The following table shows the first date and the last date for each date system and the serial value associated with each date.
But formatting dates so that they are easy to understand is equally important to ensuring correct interpretation of those results.