A method for determining an energy yield loss of a first wind turbine (1-49) of a wind farm (51) that includes a plurality of wind turbines (1-49). The first wind turbine (1-49) is operated in a reduced energy yield mode that is outside an energy-optimized normal operating mode and a reduced energy yield of the first wind turbine (1-49) is determined. At least one second wind turbine (1-49) is selected according to a pre-determinable criterion. The energy yield of the at least one second wind turbine (1-49) is determined and depending upon the energy yield of the at least one second wind turbine (1-49), an energy yield potential of the first wind turbine (1-49) is determined. The difference between the energy yield potential of the first wind turbine (1-49) and the determined reduced energy yield is formed.