One way:

Assume the Due date in cell in A1, the Completed date in B1

CF1: Formula is =AND(LEN(B1)=0,A1<TODAY())
Format1: <patterns/<red

CF2: Formula is =AND(LEN(B1)=0,A1<(TODAY()+7))
Format2: <patterns/<yellow

In article ,
Pete Sperling wrote:

One Cell contains a Due Date, and a second cell contains a Completed Date.
1. I would like to have the background of the Due Date cell to change to
yellow only when the date in this cell is within one week of todays date and
the Completed Date cell is still null, otherwise the background remains white
or transparent.
2. I would like to have the background of the Due Date Cell to change to
red only when the date in this cell is older than todays date and the
Completed Date cell is null.

Any help greatly appreciated - Pete