Situation-I need to sum all of the prior month totals, which increment over time.

I know the rows, and I can calculate the columns...

For instance, It goes from D6:I37.

But now in the next month it goes from D6:J37

I already have a method to compute the end column based on the month whos value exists in the model. IE January would be 1+3, the 1 is available elsewhere in the sheet as a manual entry of the month to compose the report, the 3 offsets it into the array.

The question is, what goes inside the Sum()?

Maybe something like...
=Sum(D6:column(Month+3)&37)

Maybe that would work in VBA or something along those lines, but not in excel...