mobile2:
One way to do this is to add the code that follows to the OptionGroup's OnClick property. Assume you've assiged option value 1 to the button for 1 month, option value 2 for 3 months, etc.
Dim datStart as Date
datStart = Me.datebox1name.Value
Select Case Me.OptionGrpName.Value
Case 1
Me.datebox2name.Value = DateSerial(Year(datStart), Month(datStart) + 1, Day(datStart))
Case 2
Me.datebox2name.Value = DateSerial(Year(datStart), Month(datStart) + 3, Day(datStart))
Case 3
Me.datebox2name.Value = DateSerial(Year(datStart), Month(datStart) + 6, Day(datStart))
Case 4
Me.datebox2name.Value = DateSerial(Year(datStart), Month(datStart) + 12, Day(datStart))
End Select
Me.Refresh
There may be other ways, but this should work.
Hope his helps,
Vic