In this chapter, the losses at the inlet and outlet are summarized and the theoretical working capacity is determined. These losses are then used to determine the efficiency of the waterwheel, which is of central importance for the design and evaluation of the overshot waterwheel as a hydropower machine. The mechanical annual energy production of the waterwheel can be calculated from the flow rate- and head-difference duration curves. The annual energy production is a key figure for determining the profitability of a particular hydropower plant site. In order to make a decision, this figure should therefore be calculated. The torque applied to the shaft of the waterwheel is also calculated. This is an important input variable for the design of the gearbox.