Electrolyte activity coefficients quantify deviations from ideal solution behavior and are central to the thermodynamics of electrochemical and separation processes. While the Debye–Hückel limiting law predicts a square-root concentration dependence at infinite dilution, experimental electrolyte data over practically relevant concentration ranges often exhibit behavior close to a cube-root dependence. The microscopic origin and extent of this intermediate concentration scaling remain unclear. In this project, Monte Carlo simulations of the restricted primitive model (RPM) will be used to investigate how electrostatic correlations and finite ion size determine the concentration dependence of electrolyte activity coefficients. Mean ionic activity coefficients will be calculated directly from free-energy simulations, without imposing a Debye–Hückel concentration dependence. Particular attention will be given to finite-size convergence at low concentrations, where long screening lengths require increasingly large simulation systems. Following validation of the thermodynamic limit, simulations will explore concentration and ion-size dependence and determine the range over which square-root, cube-root, and other effective scaling regimes emerge. The calculations will provide a controlled comparison between a minimal microscopic electrolyte model and experimental activity-coefficient data. This will help establish whether the experimentally observed cube-root regime can arise from electrostatic correlations and excluded-volume interactions alone, or whether additional molecular interactions are required.