<p>A model is proposed to estimate the number of loading cycles from the moment of fatigue crack initiation to reaching a certain critical size in specimens with a stress concentrator under a stepwise variation mode of the applied uniaxial cyclic stress range. The variation history of cyclic stress range is taken into account in the model during the transition from a larger to a smaller range, using the influence of the linear size of the plastic zone ahead of the crack tip, which was formed at a larger range, on the level of crack closure during loading with a smaller range. In addition to the loading parameters and geometric dimensions of the cross-section of the specimen and stress concentrator, the initial data for the evaluation are elastic characteristics (the elastic modulus, Poisson’s ratio, and macroyield onset stress, which are determined from tensile tests of standard specimens) and microstructure characteristics (grain size, Taylor’s factor, Burgers vector, and grain misorientation angle, which are determined from the analysis of the microstructure of the initial material). No fitting parameters or experimentally determined fatigue resistance characteristics of the material are used. The calculations of crack growth kinetics and fatigue life according to the proposed model for steel 45 specimens with a blind hole, which were loaded with a two-step uniaxial stress range under different modes of changing the level and duration of the steps, show a good agreement with the experimental results.</p>