In Hybrid Electric Vehicles, Regenerative Braking is an essential function to convert vehicle kinetic energy into electrical energy, which charges the battery during a braking event. In comparison, conventional vehicles use friction brake only and discard the kinetic energy available for later use. This paper introduces methods of evaluating Regenerative Braking Efficiency, including multiple efficiency definitions that lead to different attributes. The paper proposes regenerative brake event definitions during the FTP cycle and how they are used for control strategy and calibration updates. Also, we apply the efficiency metrics to benchmarking vehicles to compare the performance with our vehicle. The paper presents a sample comparison result. Finally, we compare our efficiency metrics with the Environmental Protection Agency (U.S.EPA) official regen efficiency evaluation process.