R0A is an important measure of diode performance. In theory, it should be possible to predict R0A from material parameters; in particular composition, carrier concentration and lifetime. We have tested this hypothesis by making diodes in fully characterized material and comparing the measured and predicted R0A. Three types of undoped epitaxial CdHgTe were used and the junctions were formed by ion beam milling. At 192 K the predicted and measured R0A values are comparable. At this temperature, diode leakage is predominantly diffusion current from the p-side of the junction and analysis of the R0A versus hole concentration data shows that Auger generation is responsible. At 77 K the situation is more complicated due to n-side leakage currents and possibly generation in the depletion layer.