A method for operating a wind power plant having at least one rotor blade, the blade angle of which can be adjusted. The wind power plant is operated with a predefinable reduced energy output set point. To determine the potential output, at least one predefinable operating parameter of the wind power plant is measured and is applied to at least one stored characteristic curve for the reduced energy output set point. The actual energy output is determined and the loss in the output is formed from the difference between the potential output and the actual energy output.