Thanks for responding so quickly. I'm glad my logic seems correct although I receive the following error when I try the proposed syntax:
"The calculation contains errors: All fields must be aggregate or constant when using table calculation functions or fields from multiple data sources "
Any thoughts appreciated.
(FYI: I am using two different excel files loaded as two different sources. They are linked using a calculated field in each source. One file is the main data file the second is the source of the "months to add")
Can you attach the packaged workbook?
Great, that works. Many Thanks