A level of power reduction for a transmitter arranged to transmit signals modulated according to one of a number of modulation configurations via radio channels in a digital wireless communications system is estimated. Modulation dependent data comprising a term calculated from a third order product of a signal modulated according to a modulation configuration are provided, and a power reduction estimate for transmission of signals modulated according to said modulation configuration is calculated there from. The modulation dependent data are provided to comprise, in addition to the term calculated from a third order product, at least one term calculated from a higher order product. Further, transmitter dependent data are provided, and the estimate is calculated from said modulation dependent and transmitter dependent data. Thus a more accurate method of determining a power reduction is achieved, which also allows different operating conditions for the transmitter to be considered.