I am trying to get a weighted average based on item cost, potential cost
increase, and peices sold. I entered a formula using sumproduct which works,
except I can't seem to figure out how to make it work for a filtered set of
data.

Column AJ = design improvement cost increase
Column AP = sold qty
Column U = item cost

=SUMPRODUCT(AJ5:AJ845,AP5:AP845)/SUMPRODUCT(AP5:AP845,U5:U845)

I am hoping to be able to filter based on a product category and see the
weighted average cost increase for a potential design improvement by category.

any help would be greatly appreciated.