MTD CALCULATIONS, PLEASE HELP

[#1]

Hi,

I am trying to calculate comparative MTD values for our GP but I have to offset previous years by one day...this is what I have but it doesn't seem to be working like I want....this is for 2008

sum

(if(YearToDate([INVC DATE],-2,month(today()),(today()-1)),[TOT REG $GP]))