The finite element alternating method, which has proved to be an extremely efficient scheme for the accurate calculation of stress intensity factors, is augmented here by an algorithm to calculate the fatigue life, under cyclic loading, of three-dimensional structural components. The alternating method involves the combination of an analytical infinite body solution with a numerical solution for the uncracked physical structure. The advantage here is that mesh generation and computational time are considerably reduced since this finite element approach only entails an analysis of the uncracked body. These simplifications make it possible to implement a three-dimensional fatigue crack growth algorithm into the alternating method. This approach has been applied here to various fatigue problems in complex aircraft components. Solutions were initially developed for constant amplitude loading and then extended to the more difficult case of variable amplitude loading.