argument for DATEADD function :
DATEADD (*datepart* , *number* , *date* )
datepart can be: yy, qq, mm, dy, dd, wk, dw, hh, mi, ss, ms
number is an expression that can be resolved to an int that is added to a datepart of date
date is an expression that can be resolved to a time, date, smalldatetime, datetime, datetime2, or datetimeoffset value.