The differential equation for an RC low-pass circuit is RC (de//0(t)/dt) plus e//0(t) equals e//i(t), where e//0(t) and e//i(t) are the output and input voltages respectively. A method for the numerical solution of the equation which requires mainly one multiplication and one evaluation of the value R for each sample is described. This is an advantage over other methods, which require a greater number of multiplication and evaluation.