Finite difference linearization of pore concentration gradient in nanofiltration membranes greatly simplifies the solution of a three-parameter model (pore radius', membrane charge, and pore dielectric constant) for electrolyte rejection by removing the requirement for numerical integration of the extended Nernst-Planck equation. The validity of the linearized model is first experimentally tested by comparing with a rigorous Characterization of the Desal-DK nanofiltration membrane, the linearized model closely agreeing with the numerical solution of the full model. Investigation of pore concentration profiles showed the assumption of linearity, to be valid over a wide range of nanofiltration conditions. The linearized model it-as also successfully extended to ternary electrolyte mixtures, highlighting its main advantage over analytic solutions. Overall, the model is a powerful tool for characterization of nanofiltration membranes and subsequent prediction of separation performance. Computational demands are modest in terms of time and complexity.