Thanks, stkneer. Your solution does work. It is a workaround but since it does what I need, I'll take it!

Richard, I'm not sure what a more "normal" layout would be. We have a variable number of "transactions" (payment amount and date) and they are not consistent in terms of frequency nor chronology. The data is more appropriately thought of as a master/child/grandchild relationship, easily handled with a database system where you can support multiple layers of one-to-many record relationships. It's really not a suitable application for a spreadsheet without a lot of rigamarole, witnessed by the fact that in order to get sktneer's solution to work, we need to "fool" the system. I am surprised that a function can't be used in an array formula - or so it seems. Or my IsNum function would have worked???