This paper introduces a calculation model for piezoelectric energy harvesters based on the frequency up-conversion method. Magnetic coupling is used to pluck a beam without physical impact. The piezo bimorph itself is modeled with a fully distributed parameter approach and then combined with a simple inverse square assumption for the magnetic forces. The results are verified experimentally and it is shown that the model is capable of reproducing the effects of various parameters, such as magnet orientation, initial gap between magnets and magnetic force.