I want to conditionally format a cell if two other cells return no value

[Tristram_ZX81]

In below picture, C column is sum of A:B. However, I want the C column to go red if there is no value in either A or B, as in row 280, 284, 285 and 288 below. However, I can only find how to conditionally format 'blank' cells. The problem is, these cells aren't blank, they have IF formula in them referring to the data in columns D onwards. So I want C to flag red if the IF formula returns no data for either column. Sometimes the A and B (and C) will return a 0 (zero); I don't want this to trigger the conditional formatting. Any ideas?

 

[Tristram_ZX81]

I applied it to C4 and then dragged the cell down to apply it to all of column C from C4 down.

 

[steve the fish]

Ok lets start from the start. Go to Home-Conditional Formatting-Manage Rules. Change the dropdown to This Worksheet. What do you see? Clear any that shouldnt be there. I need to know the formula being used and its applies to range.

 

[Tristram_ZX81]

Right now there's nothing in there. The only rules that have been in there were your above ones, which resulted in the above screen grabs, which I have since removed.

 

[Fluff]

If you are applying the Cf to C4 down use

=AND(A4="",B4="")

The cells in the Formula should match the first row in the applies to range.

 

[Tristram_ZX81]

Thanks Fluff, that works! Apologies Steve, I realise now this is the first formula you gave me, I'm not sure how I managed to misapply it.

 

[Fluff]

Glad we could help & thanks for the feedback.