I am trying to use the sumifs function to sum monthly sales by customer. The Sum Range is named Sales, Criteria Range 1 is named Dealer,Criteria 1 will be a dealer from that range, and Criteria 2 range is labeled Period and will be a date.

The formula that I have tried is:

=sumifs(Sales,Dealer,"HEBLON HTG",Period,"Jan-07")

It returns a value of zero so I've entered one of the criteria wrong, is there anything special I have to do with dates?

Any help would be greatly appreciated

Thank You