Abstract: A method and apparatus for determining the fatigue life of a structure calculate, in real time, the values for the magnitudes of the stress forces imposed at a particular location on the structure, from one or more sensed structural parameters. Also, the associated temperature values of the structure may be calculated or measured. The calculated stress data are continuously examined, in real time, to determine if the direction of their magnitude is increasing or decreasing. If a change in direction is indicated, the previously stored peak data point in the increasing direction is paired with the previously determined peak data point in the decreasing direction to form a cycle pair. The structural fatigue life is then determined, in real time, from this cycle pair.