Magnetic refrigeration is an alternative cooling technology to vapour compression. Due to the large operating space of magnetic refrigeration devices, modelling is critical to predict results, optimize device parameters and regenerator design, and understand the physics of the system. Modeling requires accurate material data including specific heat, magnetization and adiabatic temperature change, ΔT_ad. For a reversible material ΔT_ad can be attained directly from measurement or indirectly through calculation from specific heat and magnetization data. Data sets of nine MnFeP_1-xAsx alloys are used to compare calculated against measured ΔT_ad. MnFeP_1-xAsx is a promising first order material because of a tunable transition temperature, low material cost and large magnetocaloric properties. Because MnFeP_1-xAsx alloys exhibit thermal hysteresis there are four possible calculation protocols for adiabatic temperature change;​ ΔT_ad,HH, ΔT_ad,CC, ΔT_ad,HC and ΔT_ad,CH. ΔT_ad,CHdeviates the most from measured data and therefore it is assumed that this case is not representative of the material behavior. Results show ΔT_ad,HH and ΔT_ad,CC align with measured data as well as ΔT_ad,HC. The three protocols that align best with measured data have two consistent errors including a colder peak ΔT_ad and a larger FWHM. With more data sets and analysis a preferred calculation protocol may be found.