The benefits of using winglets on wind turbines has been well documented. However, adding winglets to wind turbine blades leads to significant increases in blade root bending moments, requiring expensive structural reinforcement with cost and weight drawbacks. A unique design philosophy for retrofitting winglets on existing wind turbines is presented. These retrofit winglets offer an increase in power produced without the need for structural reinforcement. Predicted performance and cost benefits are illustrated via a study using the NREL 5MW reference wind turbine. The addition of winglets resulted in a 2.45% increase in Coefficient of Power (Cp) and 1.69% increase in Annual Energy Production (AEP).