I trying to create a stats monitoring sheet and i need to calaculate the
target peiod

The target is to conduct the interview within 3 months of the start of the
month in which the interview became due.

IThe date that it is due will be given.
how do i tell excell to go back to the start of that month and then
calcualte a 3 month window from there?

Also i need both dates to be shown as the target window