Piezoelectric (PE) devices, including PE nanogenerators (PENGs) and sensors, have been extensively studied for applications that require the transduction of mechanical and electrical energy. Recently, the need for flexible and responsive mechanical-to-electrical transducers has ignited a widespread trend in developing electromechanically active polymers. However, reports detailing the electrical characterisation of such materials have given insufficient attention to the influences of static energy (i.e., triboelectricity (TE)) in the electrical outputs reported. Separating PE and TE contributions is complex, as both occur due to mechanical motion and the waveform of the output signal is exceptionally similar. In this work, the popular frequency domain analysis technique – the fast Fourier transform (FFT) is used for the first time to decouple the energy contributions of PE and TE nanogenerators by comparing a polyvinylidene difluoride (PVDF) PENG against a non-PE polyimide (PI) NG. The intensity and the bandwidth of PE and TE signals, relative to the excitation frequency, enabled rapid identification of TE contributions in the PE measurements. This method will enable the accurate development of PE devices with precise electrical outputs in the future.