Activation energies are critical to a mechanistic understanding of electrochemical reaction processes. However, significant challenges such as cell-size dependence pose a challenge to determining accurate ab-initio electrochemical barriers. In this work, we suggest a simple model to compute the charge transfer coefficients, and hence the activation energies, with just a single DFT calculation. Our method builds upon previous extrapolation procedures and removes the short-comings of explicit partitioning of the charge density, which give rise to ambiguous or unphysical jumps in charge transfer along the reaction pathway. We show that the charge transfer coefficient is related to the derivative of the atom centered forces with respect to applied field. We perform a series of electrochemical barrier calculations and show that the charge transfer coefficient computed with our method is in good agreement with the value obtained by performing traditional cell-extrapolation procedures, which require multiple cell sizes. We show that our methodology can be successfully used for transition states as well as polar adsorbates, both critical species in electrochemical reactions.