Lesnicar and Marquardt introduced a modular multilevel converter (MMC) topology back in 2003. Although this topology has received a great deal of attention in recent years by both the research community and industry, hitherto no steady-state model has been developed which accurately captured all the relevant power losses while being computationally light. Hence, the aim of this paper is to introduce a fast MMC loss model which captures the key sources of power losses in steady-state operation. The proposed model was compared to a loss model developed by Marquardt. Both models presented similar results under the same assumptions. However, the proposed model captures the switching losses more realistically and considers the temperature of operation of the electronics, as well as the losses of the inductors and cooling system, in the overall efficiency of the MMC. To validate these new additions, the proposed steady-state model was compared to a dynamic model. Once again, the proposed model was able to capture the different sources of power losses. Nonetheless, results demonstrated that the balancing strategy greatly influences the efficiency of the MMC. Therefore, information regarding the envisioned control strategy is necessary to accurately calculate the efficiency curve of the MMC.@en