This paper proposes a new approach for determining the low-speed boundary at which regenerative braking capability of Electric Vehicles (EVs) is still effective. The regenerative braking boundary at low speeds depends on many different factors influenced by driver behavior and driving conditions that are challenging to measure and predict. Thus, utilizing a lookup table, which covers various operating conditions, can be an effective method to dynamically determine this boundary. In the proposed method, the performance of the electric motor and its controller are extracted for different operating points and the results are stored in a lookup table. The motor performance curve obtained from this lookup table is then utilized in the vehicle brake controller to define the regenerative braking boundary and accurately adjust the blending of regenerative-and friction-based brakes with the goal of maximizing energy extraction. A MATLAB/SIMULINK model that represents the vehicle electric motor and road-load conditions is utilized to validate the effectiveness of the proposed approach. The results show an increase in the harvested energy compared to a case where a constant low-speed threshold is taken into account in the brake controller.