Rotor-end factors are dimensionless quantities used in designing the solid-rotor induction motors to approximate the effects of finite length. It is well known that there are a few analytic estimates of these factors available. With certain, generally acceptable accuracy these match most of the configurations of motors with uniform rotors, but are not adequate for those containing axial slits. In this work, an appropriate three-dimensional model is proposed to numerically evaluate the factors of the rotor-end effect for the uniform (unslitted) and the axially slitted rotors having slits through the whole length. For the two cases these factors are expressed via ratios taken between the rotor powers calculated in three- and two-dimensional systems of coordinates, and are expressed as functions of frequency. The rotor-end factors obtained in such a way are different for the unslitted and slitted rotors. A notable improvement of accuracy is obtained in comparison with the traditional methodology when the numerically evaluated end-factors are used in the two-dimensional circuit-driven frequency-domain finite-element model to determine the motor characteristics.