Summing below vlookup from an Index Array

Hi All,

Im looking to create a formula that would sum the above values to get a total.I have used a drop down list and an Index Array along with Vlookup to get the monthly sales per product per customer.

My thoughts were that if I add an If function to the start of my vlookup formula to say that when it looks at the product code in Col A and if a product code is present then it must return the corresponding sales value or is the value is " " then it would sum all the sales data above it across all the monthly columns.

If you guys see any issues with my current formulas please let me know as well.

Any thoughts?

Thanks in advance.
Rob.