To sum Row 2, starting at A2, and user enters the number of columns to total
into A1:

=SUM(A2:INDEX(2:2,A1))

If A1 is empty, entire row will total.

To sum Column B, starting at B1, and user enters the number of rows to total
into A1:

=SUM(B1:INDEX(B:B,A1))
Same holds true if A1 is empty.

To allow user to define both start and end points, entering boundaries in
say A1 and A2 for Column B:

=SUM(INDEX(B:B,A1):INDEX(B:B,A2))

--
HTH,

RD

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"SD" wrote in message
...
I am building a financial model and would like to sum values over a
variable
number of preceeding cells (the number of cells should be inputted by a
user). How can I implement this functionality?