Performance of cathodic protection system in reinforced concrete structures is generally evaluated using 100 mV decay cri-terion. This approach is widely used, however has its own limitations. Recently, a new approach by determining the actual corrosion rate using the Butler Volmer equation has become an ‘alternative’ criterion for assessing the performance of cathodic protection system. This paper deals with critical examination and practical application of Butler-Volmer Equation to judge the effectiveness of cathodic protection system. Sensitivity analysis of various input parameters through numerical modelling by parametric studies showed significant dependence of corrosion rate on cathodic Tafel slope. One-year field data from a cathodic protection monitoring site in UK was collected and variability in the two approaches was assessed.