A static model is introduced, which allows for the estimation of the performance of a full scale EBPR plant. The model is based on the assumption that the readily biodegradable substrate from the influent and the total COD-turnover in the anaerobic zone determine the amount of phosphorus contained within phosphorus accumulating organisms. Model predictions are based on wastewater composition, operating temperature, effects of oxygen and nitrate addition to the anaerobic reactor, solids retention time and anaerobic mass fraction of the activated sludge. The model is calibrated with full scale experience and may be useful for the analysis of plant performance as well as the design of new treatment plants.