In my worksheet there are 4 columns - A, B, C, D.

If no date is entered in Column B 90 days after entering a date in Column A - Column B should be flagged up (conditional formatting I think).

&

If no date is entered in Column C 90 days after entering a date in Column B - Column C should be flagged up

&

If no date is entered in Column D 90 days after entering a date in Column C - Column C should be flagged up.

Is there a way of doing this? I have googled around but nothing that works for what I need above.

Any help would be greatly appreciated. I'm using Excel 2007.