Dynamic Sumproduct Lookup

Hi All,

I am trying, what I thought was going to be easy, to do a sumproduct, but trying to lookup the variables.

Here is what I mean.

In Row 1, starting in Column B is the month.year. In Column A, starting in Row 2 is the customer. There can be hundreds of customers and the month.year can very in the raw data.

I want the formula to find the month.year then add up all the values where it sees the customer name. I normally would use a sumproduct because it would be a column for column reference, but I don't know which column the date may fall in on the data page.

Attached is a sample. Summary is where the formula takes place.

Thoughts?

Thanks,
Matt