VBA code for triggering a macro based on change in cell with formula

Th0r_L13n 

The best option is to check the cells that determine the result of the formula and that are directly changed by the user.

A very simple example: let's say that cell A10 contains the formula =SUM(A2:A9), and that A2:A9 are filled by the user. Instead of checking A10, check A2:A9:

Private Sub Worksheet_Change(ByVal Target As Range)
    If Not Intersect(Range("A2:A9"), Target) Is Nothing Them
        ...
    End If
End Sub

Alternatively, you could use the Worksheet_Calculate event. This will cause a lot of overhead, though, for this event does not have a Target argument. So the code will run every time any cell on the sheet is recalculated.