If Due date is in cell A1, enter this formula in the box where Excel allows
you to enter your own formula.
=A1EDATE(A1,-6)
Format = Green

=A1EDATE(A1,-3)
Format = Red

"FC" wrote:

I' like to find a formula to do conditinal formating for cells with no colors
containing dates to turn green when is 6 month before a due date ( with a
reference date), and red when is 3 month before.
Also in different sheet I need a formula that gives me the date of 9 months
ahead of a reference date in another cell. Thank you very much.