Isotropic hardening characterizes the expansion or compression of the yield surface due to material property changes. It depends on the number of cycles and not on how often it occurs or strain rate. In the fatigue design eN procedure, the transient of hardening or softening in the cycles is not considered, it is assumed that the material has stabilized in steady state since the first cycle. But in projects for short lives, it is important that the transient is taken into account, as it can affect the strain ranges and stress peaks. From data obtained experimentally for 1020 steel and annealed 7075 aluminum, a routine will be created through the MATLAB software where a model will be made from three solutions of the Voce equation that will approximate the Ramberg-Osgood model.