An innovative approach for predicting the reliability of a structure that is subject to a variable‐amplitude dynamic load is presented. In this approach, a Gassner durability curve with its scatter is modelled using a 2‐parametric Weibull's probability density function (PDF). The trend of the Gassner durability curve is modelled with a general hyperbola equation in a log‐log scale. The hyperbola equation is applied to represent the durability curve for the 63.2% probability of fatigue failure that describes the dependency of the Weibull's scale parameter on the loading spectrum's maximum stress. Equations are derived to link the parameters of the hyperbola curve to the material's S‐N curve and the loading spectrum. The Weibull's shape parameter is estimated from the scatter of the material's S‐N curve. The proposed Gassner‐curve model is applied to calculate the fatigue reliability from the PDF of the loading spectrum's maximum stress and the PDF of the durability‐curve's amplitude stress for the selected number of loading‐cycles‐to‐failure.