Risk evaluation for fatigue failure of the engineering components is an important aspect of the engineering design. This study presents a probabilistic model for calculating Weibull distribution parameters to reduce the effect of percentage discretization error of experimental fatigue life and R-S-N curves for three reliability levels. The results show some error reduction in the Kolmogorov-Smirnov test and R-square values. Also, the Basquin model is used for different reliability levels with the same error order. The coefficient of variation for fatigue life increases at higher stress levels and has a linear relation with stress level for a high-cycle fatigue regime.