TODAY
Returns the serial number of the current date. The serial number is the date-time code used by the spreadsheet for date and time calculations.
Syntax
TODAY( )
Remark
Dates are stored as sequential serial numbers so they can be used in calculations. By default, December 31, 1899 is serial number 1, and January 1, 2008 is serial number 39448 because it is 39,448 days after January 1, 1900.
Note If you want to change the display of the result from
a serial number to a date format or vice versa, select the cell and click Commands
and Options 
on the
toolbar.
Click the Format tab and then select the format you want in the Number
Format box. To view the date as a serial number, apply the General
number format.