Firs Off Thanks For All your help.
I have the folowing Lay Out
A B C D E E F
1 Actual Apr
2
3 Part Jan Feb Mar Apr May YTD
4 G115 100 100 300 500 300
5 G116 0 500 200 200 200
6 G117 200 500 300 200 500
7 G118 300 0 0 200 500

I need the Ytd coulum to sum the sales in base of Cell B1 that will be
updated, in this case i need the total YTD sales For Apr.

I think it has somthing to do with Sum(offset()) but i dont know how.