About dates and date systems

Microsoft Excel stores dates as sequential numbers which are called serial values. By default, 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. 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. You can view a date as a serial value and a time as a decimal fraction by changing the format of the cell that contains the date or time to General format.

Because the rules that govern the way that any calculation program interprets dates are complex, you should be as specific as possible about dates whenever you enter them. This will produce the highest level of accuracy in your date calculations.

Excel supports two date systems: the 1900 and 1904 date systems. The default date system for Microsoft Excel for Windows is 1900. The default date system for Microsoft Excel for the Macintosh is 1904. You can change the date system. On the Tools menu, click Options, click the Calculation tab, and then select or clear the 1904 date system check box.

The date system is changed automatically when you open a document from another platform. For example, if you are working in Excel for Windows and you open a document created in Excel for the Macintosh, the 1904 date system check box is selected automatically.

The following table shows the first date and the last date for each date system and the serial value associated with each date.

Date system	First date	Last date
1900	January 1, 1900 (serial value 1)	December 31, 9999 (serial value 2958465)
1904	January 2, 1904 (serial value 1)	December 31, 9999 (serial value 2957003)

To ensure that year values are interpreted as you intended, type year values as four digits (2001, rather than 01). By entering four digits for the years, Excel won't interpret the century for you.

For Microsoft Windows 2000 or later

If you are using Microsoft Windows 2000 or later, the Regional Options in Windows Control Panel controls how Excel interprets two-digit years.

For dates entered as text values

When you enter a date as a text value, Excel interprets the year as follows:

00 through 29 Excel interprets the two-digit year values 00 through 29 as the years 2000 through 2029. For example, if you type the date 5/28/19, Excel assumes the date is May 28, 2019.
30 through 99 Excel interprets the two-digit year values 30 through 99 as the years 1930 through 1999. For example, if you type the date 5/28/98, Excel assumes the date is May 28, 1998.