We present a comparison of experimental and simulated frequency-and field-domain electron paramagnetic resonance (EPR) spectra of integer and half-integer high-spin transition-metal ion complexes. For the simulation of EPR spectra a new tool within the EPR simulation software Easy Spin is introduced, which allows for field- and frequency-domain EPR simulations with the same theoretical model and the same set of spin Hamiltonian parameters. The utility of this approach is demonstrated on the integer-spin complexes NiBr2(PPh3)(2) and [Tp(2)Mn]SbF6 (both S = 1) and the half-integer-spin Fe(III) porphyrins, hemin (Fe(PPIX)Cl) and Fe(TPP)Cl (both S = 5/2). We demonstrate that the combination of field- and frequency-domain EPR techniques allows the determination of spin Hamiltonian parameters, in particular large zero-field splittings, with high accuracy.