A major challenge in the theoretical treatment of electrochemical charge transfer barriers is that simulations are performed at constant charge, which leads to dramatic potential shifts along the reaction path. Real electrochemical systems, however, operate at constant potential, which corresponds to a hypothetical model system of infinite size. Previous studies of hydrogen evolution have relied on a computationally costly scheme that extrapolates the barriers calculated on increasingly larger cells, and extension of this scheme to more complex reactions would be prohibitively costly. We present a new method to determine constant potential reaction energetics for simple charge transfer reactions that requires only (1) a single barrier calculation in an electrochemical environment and (2) the corresponding surface charge at the initial, transition, and final states. This method allows for a tremendous reduction in the computational resources required to determine electrochemical barriers and paves the way for a rigorous DFT-based kinetic analysis of electrochemical reactions beyond hydrogen evolution.