I am also looking to do a sumproduct of sorts, basically I need to take a proportion from previous months, with a multiplier from the current month. With months left to right in Excel the formula looks like this SUMPRODUCT(N2/C5:M5,C6:M6). N2 is the multipier from the current month, row 5 the volumes and row 6 the proportions to take through. is this possible without creating lots of rows and summing them? I have one example which needs to use 5 years, so splitting the formula out would be very long and messy.
Any advice would be gratefully recieved!