I would look at using DateAdd
and DateSerial
.
So an expression like:
=DateAdd(DateInterval.Month
, 1
, DateSerial(Parameters!Year.Value, Parameters!Month.Value, 1))
This uses DateSerial
to construct the first of the month for the selected Year and Month, then uses DateAdd
to add another month to this.
Worked fine on a basic report I made to test the expression: