@MONTH

@MONTH[mm-dd-yy]:  Returns the month number for the specified date (1-12). 
 MONTH uses the date format and separators mandated by your country code 
(for example dd.mm.yy in Germany, or yy-mm-dd in Japan). The year can be 
entered as a 4-digit or 2-digit value.  Two-digit years between 80 and 99 
are interpreted as 1980 - 1999; values between 00 and 79 are interpreted 
as 2000 - 2079.