The total value of the separative work provided by separators in a step cascade, in which mixing cannot be avoided, is larger than that provided by a corresponding ideal cascade operated under the same conditions (rate and concentration) of product, feed and waste. This difference in the separative work is due to mixing loss. In this study, a method for calculating the mixing loss in a step cascade is proposed, in the case where the separation factor is nearly 1. Calculations using this method reveal that in each step there exists a stage at which no mixing takes place, provided that the value of the cut in the step is nearly the value of the cut minimizing the mixing loss in the step. As the value of the cut in the step deviates from the value of the cut minimizing the mixing loss in the step, the position of the mixing free stage shifts upwards of downwards from mid-position of the step.