In this paper, we present a method for turbo codes (TC) performance prediction, in terms of bit error rate (BER) and frame error rate (FER) versus signal to noise ratio (SNR), when they are used with high-order modulations (HOM). The method is based on two simplifying hypotheses and assumes that the BER/FER vs. SNR performance, in the case of BPSK modulation, is known. For the simulations we have chosen the double-binary turbo codes (DBTC) used in the DVB-RCS standard. The experimental results confirm the good accuracy of the proposed prediction method and validate our assumptions. The method has been applied in the case of 16-Quadrature Amplitude Modulation (16-QAM), but it can be easily extended to any other type of modulation.