We present a numerical approach to simulate the Ferromagnetic Resonance (FMR) of micron and nanosized magnetic elements by a micromagnetic finite di?erence method. In addition to a static magnetic field a linearly polarized oscillating magnetic field is utilized to excite and analyze the spin wave excitations observed by Ferromagnetic Resonance in the space- and time-domain. Our continuous wave approach (CW) provides an alternative to the common simulation method, which uses a pulsed excitation of the magnetic system. It directly models conventional FMR-experiments and permits the determination of the real and imaginary part of the complex dynamic susceptibility without the need of post-processing. Furthermore not only the resonance fields, but also linewidths, ellipticity, phase relations and relative intensities of the excited spin wave modes in a spectrum can be determined and compared to experimental data. The magnetic responses can be plotted as a function of spatial dimensions yielding a detailed visualization of the spin wave modes and their localization as a function of external magnetic field and frequency. This is illustrated for the case of a magnetic micron sized stripe.