See the thread two posts earlier than yours, "Counting using multiple criteria"
http://www.excelforum.com/showthread...hreadid=497726
You'll use a sumproduct of two true/false arrays.

"JEFF" wrote:

Hello,

I have worksheet with customer names in column A, and the units purchased by
month in consecutive columns beginning in column B. I would like the user to
use an input cell that determined the time frame (in months). Thus, if they
put "10" in the input cell, a formula would return the number of times the
customer purchased in the last 10 months.

I am comfortable using OFFSET, but not with a COUNT function..... Any ideas?

TIA!