There is a strong need in the power electronics community to have design tools capable of performing simultaneous simulations in different domains, e.g. electric, magnetic, dielectric and thermal. Therefore, this paper presents an approach to the calculation of both semiconductor and magnetic core losses in a common simulation environment. The model of a magnetic component, such as transformer, is chosen to be permeance-based and rests on hysteresis modeling. The simulated circuit combines a full-bridge LLC resonant converter, whose transformer is based on electrical and core specifications of a 100 kW, 10 kHz already realized medium frequency transformer prototype. The paper demonstrates that solely with information about the geometry, used material and electrical ratings of the transformer, it is possible to accurately estimate its core losses, allowing for their inclusion into system level simulations.