A simple non-iterative method for calculating the potential of an electric double layer is developed. The method is presented here within the framework of the hypernetted chain (HNC) approximation. However, the basis of the method is general so that applications to other approximations are possible. The method is based on the Henderson-Blum equation for the contact value of the density profile and on the fact that even though the HNC potential differs significantly from the Poisson-Boltzmann (PB) potential, the HNC density and charge profiles differ only slightly from the corresponding PB profiles. The agreement of the HNC potential, calculated by this method, with the results of more elaborate iterative calculations is good. © 1980 Elsevier Sequioa S.A.