The invention relates to a method for determining a torsional moment of a wheelset shaft of a rail vehicle during the operation of the rail vehicle. The wheelset shaft has a shaft and two wheels secured to ends of the shaft, said wheels being provided for rolling on two rails. A model is used to calculate a torsional moment which acts on the wheelset shaft, and the model is based on a torsional vibration of the wheelset shaft at a specified slip action point. The torsional moment acting on the wheelset shaft is ascertained using the energy of the torsional vibration of the wheelset shaft at the slip action point and using a damping energy which acts on the torsional vibration of the wheelset shaft.