We present a method of a numerical golden rule calculation for single electron transistor (SET) simulations. This golden rule calculation is, in principle, accurate within the semiclassical framework and is easy to implement. The usefulness of the calculation is demonstrated through the comparison of the current-voltage (I-V) curves for a SET simulated using results of this numerical golden rule calculation with the T-V curve simulated using results of the so-called basic golden rule calculation.