Intermodulation distortion is one of the key design requirements of Radio Frequency circuits. The standard approach for analyzing distortion using circuit simulators is to mimic measurement environments and compute the response due to a two-tone input. This considerably increases the CPU cost of the simulation because of the large number of variables resulting from the harmonics of these two tones and their intermodulation products. In this paper, we propose an analytical method for directly obtaining the intermodulation distortion from the Harmonic Balance equations with a only single-tone input, without the need to perform a Harmonic Balance simulation. The proposed method is shown to be significantly faster than traditional simulation based approaches.