Computational model of a proton exchange membrane (PEM) water electrolyzer is developed to enable investigation of the effect of operating conditions and electrolyzer components on its performance by expending less time and effort than experimental investigations. The work presents a dynamic model of a PEM electrolyzer system based on MATLAB/Simulink software. The model consists mainly of four blocks – anode, cathode, membrane and voltage. Mole balances on the anode and cathode blocks form the basis of the model along with Nernst and Butler–Volmer equations. The model calculates the cell voltage by taking into account the open circuit voltage and various over-potentials. The model developed predicted well the experimental data on PEM water electrolyzer available in the literature. The dynamic behavior of the electrolyzer system is analyzed and the effects of varying electrolyzer temperature and pressure on electrolyzer performance and over-potentials are presented. ► PEM water electrolyzer (PEMWE) modelled in Matlab/Simulink to capture the dynamic behaviour to some extent. ► Model predicts experimental data well on performance of PEMWE at different temperatures. ► Model results show operating temperature and pressure have opposite effects on performance. ► Operating temperature, pressure and performance of PEMWE have to be optimized for pressure require to store hydrogen. ► Ohmic overvoltage increases sharply with current density indicating improvement in performance possible by using low resistance electrolyte.