A systematic study of the inverse magnetocaloric effect (IMCE) in Ni50Mn35.8Sn14.2 and Pr0.5Sr0.5MnO3 has been performed to understand the impacts of first-order phase transition (FOPT) and phase coexistence on the universality of the temperature-dependent magnetic entropy change, ΔSM(T). We show that for Ni50Mn35.8Sn14.2—a system exhibiting IMCE associated with FOPT—it is possible to construct a universal master curve to describe ΔSM(T) in different applied fields without rescaling a temperature axis. However, the universality of IMCE does not hold for Pr0.5Sr0.5MnO3—a system with coexisting ferromagnetic and antiferromagnetic phases. The proposed universal curve provides a simple method for extrapolating ΔSM in a wide range of fields and temperatures, thus giving useful guidance to the design of magnetocaloric materials for active magnetic refrigeration technology.