An apparatus and method for determining grain loss of a harvesting machine. The harvesting machine has a crop-separating region with separating members. The separating members each have separation sensors for generating a signal corresponding to the crop quantity separated. This signal is delivered to an evaluating unit for further processing. Processing includes determining a separation curve for at least some of the separating zones and converting the separation curve to a characteristic quantity. From this measured characteristic quantity, a loss is determined based on a characteristic curve deposited in the evaluating unit. By avoiding direct loss measurement on the harvesting machine, the negative crop-related effects on determining grain loss are considerably reduced.