Structural dynamics relates the excitation profile to the dynamic loads at a particular location of the structure. Spectral methods fatigue-life estimation is based on the assumptions of stationarity and the Gaussianity. This research proposes a method for a fatigue-life estimation for non-stationary excitation. The method is based on the short-time spectral narrowband method, where the short-time width was found to be related to the structural dynamics (i.e., natural frequency, damping) of the excited structure. A detailed numerical and a real experiment shows a significant accuracy increase for fatigue-life estimation at non-stationary and non-Gaussian excitation.