Summing a variable range of Columns

I have built a Sales Forecast Summary spreadsheet for a small business. One of the data column sets was each MONTH of sales. At the end (Column 13) I put a YTD with a sum across. I compared LastYTD with CurrentYTD. Last year was first year using it, so there was no "Last"Year when initially using it .

So now, ALL of last year is filled in, so the "Year To Date, Last Year" is a total summary of all 12 months. Meaning . . . . YTDthis = SUM( Jan to -Feb) But comparing Last Year's to Date, it's YTDlast=Sum(Jan to Dec)

So how do I make a function that Sum's a series of Columns that is variable, say to the Month. (I have a drop down to select which month I'm in)

So it would be something like

SUM(Column1 to ColumnX) Where X is the variable (which will change each month)

Any thoughts????

Does anyone have any thoughts on this one?

As I understand, you want something like this:

YTD 2005: =SUMIF($B$2:$L$2,"<>0",B2:L2)
YTD 2004: =SUMIF($B$2:$L$2,"<>0",B3:L3)

Year...Jan...Feb...Mar...May...Jun...Jul...Aug...Sep...Okt...Nov...Dec...YTD...
2005..12...23...................................................................................
2004..11...22......33.....44....555...66..77.......88...99....1.0....112....

Ola Sandström