Hi,
if you want to work with hidden key figures - which is not what I suggested - then you need to set the plan key figure to "data entry enabled", define the formula, use a reverse formula and set this also to data entry enabled. go to SAP help to read about usage of reverse formulas.
but this seems to me quite complicated.
what I meant is creating a restricted key figure,
make it data entry enabled
define Variable - probably for cube and value type (and maybe more char depending what is different between actuals and forecast)
depending on the month the variables either select what defines actuals or what defines forecast.
But you will need 12 sets of those variables.
If I think about it, maybe the reverse formula is not such a bad idea.
regards
Cornelia