In today's global market, considering customer needs in all changing business practices is a key tool to build strong competitive advantages. At the same time, with respect to lean manufacturing system, the current conventional costing methods are out of date. This study sets a framework that integrates Time-Driven Activity-Based Costing (TDABC) in a lean environment in a condition where shared resources are still present. The objective of this study is computing accurate product unit cost to support the lean manufacturing system to strengthen the competitive position. This case study is applied on one factory of a multinational manufacturing company operating in Egypt that moved to lean manufacturing recently. TDABC method is suggested to calculate a more accurate product unit cost for one of the factory products.