Microsoft Office Tutorials and References
In Depth Information
Excel supports dates from January 1, 1900, through December 31, 9999 (serial number =
You may wonder about January 0, 1900. This nondate (which corresponds to date serial
number 0) is actually used to represent times that aren’t associated with a particular day.
This concept becomes clear later in this chapter (see “Entering times”).
To view a date serial number as a date, you must format the cell as a date. Choose Home ➪
Number Format. This drop-down control provides you with two date formats. To
select from additional date formats, see “Formatting dates and times,” later in this chapter.
Choose Your Date System: 1900 or 1904
Excel supports two date systems: the 1900 date system and the 1904 date system. Which system you
use in a workbook determines what date serves as the basis for dates. The 1900 date system uses
January 1, 1900, as the day assigned to date serial number 1. The 1904 date system uses January 1,
1904, as the base date. By default, Excel for Windows uses the 1900 date system, and pre-2011 versions
of Excel for Mac use the 1904 date system.
Microsoft made a change. Excel 2011 for Mac uses the 1900 date system by default. Presumably subsequent Mac
versions will as well.
Excel for Windows supports the 1904 date system for compatibility with Mac i les. You can choose the date system
for the active workbook in the Advanced section of the Excel Options dialog box. (It’s in the When calculating this
workbook subsection.) Generally, you should use the default 1900 date system. (The examples in this chapter use
the default 1900 date system.) And you should exercise caution if you use two different date systems in workbooks
that are linked. For example, assume that Book1 uses the 1904 date system and contains the date 1/15/1999 in
cell A1. Assume that Book2 uses the 1900 date system and contains a link to cell A1 in Book1. Book2 displays the
date as 1/14/1995. Both workbooks use the same date serial number (34713), but they’re interpreted differently.
One advantage to using the 1904 date system is that it enables you to display negative time values. With the 1900
date system, a calculation that results in a negative time (for example, 4:00 PM–5:30 PM) cannot be displayed.
When using the 1904 date system, the negative time displays as –1:30 (that is, a difference of 1 hour and 30
You can enter a date directly as a serial number (if you know the serial number) and
then format it as a date. More often, you enter a date by using any of several recognized
date formats. Excel automatically converts your entry into the corresponding date serial