Trying to create the following Excel formula in JasperSoft: Ad Hoc Views.
=Total Gross Cost/Total Members/Months*12
Do you mean Total Gross Cost/(Total Members*Number of Months*12)?
To find Number of Months, I would try something like Year(Max(Date))*12+Month(Max(Date)-Year(Min(Date))*12-Month(Min(Date)). You might have to cast the Year and Month as integers