A method for determining an energy yield loss of a first wind turbine of a wind farm that includes a plurality of wind turbines. The first wind turbine 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 is determined. At least one second wind turbine is selected according to a pre-determinable criterion. The energy yield of the at least one second wind turbine is determined and depending upon the energy yield of the at least one second wind turbine, an energy yield potential of the first wind turbine is determined. The difference between the energy yield potential of the first wind turbine and the determined reduced energy yield is formed.