In this study, the classical strengthening equations for weak and strong particles are advanced to account for oblate-shaped γ'' precipitates in Inconel 718. The model is verified on quantitative stereology of size and distribution for both shearable and non-shearable mechanisms. The evolution of precipitation strengthening of aged superalloy Inconel 718 is simulated. In addition to precipitation strengthening, contributions of solid solution strengthening and the grain size effect are considered. Simulation results indicate a sound prediction of the final yield strength based on the presented model.