My bad. You did mention formula update, but I had missed it. '
This will not work as value changed by formula will not trigger it
This will trigger if a value is updated by formula
Private Sub Worksheet_Calculate()
How ever looking at your example,I would say the you need to trigger the source of change
Lets say that your C125 formula is A125 + B125
Then you trigger your recalc routine when A125 or b125 changes