The need for market assessment techniques and tools to analyse the product sales is increasing every day. Patents, along with gold standard therapies, play a critical role in the pharmaceutical industry in determining product sales. However, once genericized, the existence of multiple products for same molecule is a situation unique to the pharmaceutical industry. With the growing need for new methods of evaluations for mature products (Products with generic competition), the Evolution Index which is used to determine the performance of the product needs to be redefined and customised. Extrinsic factors like market dynamics influence company profitability and hence there is need for a heuristic approach to evaluate its performance. Considering the effect of competition on product performance in relation to market factors provides an optimized indicator to design an effective strategy. The newly constructed formula eliminates bias by incorporating molecule level growth and its influence on the overall portfolio of a company, especially for mature products. The new evolution index "mEI" serves the realistic picture of current market scenario and enables the companies to take a better decision based on existing competition.