Weeks-Chandler-Andersen (WCA) perturbation theory is used to develop a model for calculating solid-liquid equilibria in Lennard-Jones (LJ) systems. This LJ-WCA model has two components: an equation of state for LJ liquids derived in this work, and an equation of state for LJ solids derived previously) The model is demonstrated to capture the solid-liquid equilibria for pure argon and pure krypton, including the melting and density data.