What do you mean 'doesn't always' ?
To me that says sometimes it DOES work.
So in which cases DOES it work, and which cases does it NOT work?
And what does Not Work mean?
Do you get an error? What error?
Do you get the wrong result? What result DO you get? What result did you expect?
What do you actually expect the formula to do ?
The formula you posted isn't even complete, though I'm sure that's just a result of you manually typing it into the thread, instead of just copying it from Excel to the Thread.
=IF(AM3="","",IF(AO4="",(($Q$3*$Q$7-$Q$3)+$Q$5)*0.92-(($Q$3*$Q$7-$Q$3)+$Q$5),IF(AX4=0,AJ2*T4,AW4*T4))) This should result in a blank cell like the first formula, but instead it continues to process the calculation.
The logical conclusion is that the first formula is not doing exactly what you think it is.
AM3 is probably not really blank, but it just looks blank.
So the AM3="" condition is actually FALSE, and the formula is returning the contents of AM3.
But the contents of AM3 'appears' to be blank, but it's really not.
Maybe it contains a space, or a 'hard return' or some other strange character.