Quarterly Sums in Horizontal ???

[sirafs]

I have seen too many projections done this way for there not to be a good way of calculating this. It is driving me crazy trying to figure it out.

I have a spreadsheet that is for financial projections for a start-up. It uses months # 1 to 48 instead of real dates and is laid out horizontally. The month number is at the top and the data (a person's salary, a revenue source, etc.) is listed below that.

I have monthly data and need to have a summary page that shows quarterly values. For example, the first cell would be =SUM(C12:E12) and the cell to the right would be =SUM(F12:H12). I tried setting the column values manually for a few cells and then dragging it to a bigger range, but it ends up only changing the start of the range by 1 month instead of 3 months.

I know how to get it to do subtotals every 3 cells under the monthly data, but I can't figure out how to get them to be next to each other without manually setting the range of each sum.

THANK YOU FOR YOUR HELP!

 

[sirafs]

BTW - I can do something like =HLOOKUP(6,C1:N21,21,0) where 6 is the month number (3, 6, 9, etc) if I put the quarterly data as a row in every 3 cells.

I just want to do fully calculated in the one place so I don't have a bunch of intermediate calculation rows I have to leave in the spreadsheet.

THANKS!