Estimating a system's complexity is essential before making a decision about the architecture to be built or not. Especially for mobile User Equipments (UE) complexity is a big issue. Reduced complexity, mainly meaning reduced number of additions and multiplications in a system, is highly desired also to minimize power consumption. In order to be able to compare different systems and architectures, a figure of merit for the complexity of each specific system has to be introduced. For single rate systems usually the number of operations needed for one output sample can easily be calculated. For multirate systems this task is not that trivial, as operations have to be done on different sampling rates. This paper introduces methods for gaining figures of merit of complexity for multirate systems and proposes a novel method which is believed to be best suited.