Thanks so much for the reply. I think we're close but not quite there. This is what I converted what you wrote to based on specs of what I needed:
=IIf (Fields!PgMidAnnual.Value > 0, Fields!EmAnnual.value MOD Fields!PgMidAnnual.value, 0)
But, this is the error I get. The report renders but there's an "Error#" printed in the cell where this expression resides. This is what the error list text is reading:
Warning 1 [rsRuntimeErrorInExpression] The Value expression for the textrun ‘Textbox23.Paragraphs.TextRuns’ contains an error: Attempted to divide by zero.