In this work, a multiaxial fatigue model recently developed by members of the Fatigue, Fracture and Materials Group of the University of Brasília is applied to estimate fatigue crack initiation lives of a notched shaft. This model is based on a combination of deviatoric strain amplitudes as a measure of equivalent shear strain amplitude. In addition, the effects of hydrostatic stresses and mean deviatoric stress on fatigue life are also taken into account. Available fatigue tests conducted on SAE 1045 steel notched shafts subjected to bending and torsion were used to assess the life estimation capability of the model. Elastic-plastic finite element simulations of the notched shaft were employed to obtain the stabilized stress and strain histories at the notch root. Chaboche's kinematic hardening model was used to describe the elasto-plastic material behavior. For most of the experimental data, life estimates were within a factor of 3 in fatigue life.