A simple model based on changes in filter resistance and active area of the membrane has been used to model viral filtration. Viral particles have been modeled as colloidal particles disregarding any specific interaction and considering only passive transport in the system. The model is based on the assumption that purely steric interactions determine the ratio of concentration of viral particles inside the pore to concentration in solution at the pore mouth. Viral particles rejected by the membrane form a layer of high concentration near the membrane and this layer offers additional resistance to filtration. The membrane flux has been calculated by applying Darcy's law. The overall model involves use of six unknown parameters to account for cake formation, nature of virus, interaction between the virus and the membrane, and pore size. The breakthrough of the model virus, bacteriophage phi X-174, through normal-flow virus filters using commercial process fluids has been chosen as the system used for model validation. The model has been fitted to the time profile of flux and the log reduction value (LRV) of viral particles across the different types of commercially available filters. The model will be useful when performing studies using scale down models for correlating LRV to flux decline. The model also provides us insights into the underlying mechanisms behind viral clearance achieved from the various commercially available viral filters. (C) 2014 Elsevier B.V. All rights reserved.