Additive Manufacturing (AM) techniques have revolutionised the manufacturing processes across various applications. However, the process parameters greatly impact the mechanical properties of AM components. An understanding of the mechanical characteristics of AM components, particularly fatigue life, is necessary. This study is about predicting the S–N curve corresponding to the rotational bending test of an AM component. An endurance limit-based approach, modified with a defect factor was used to develop the S–N curve. The defect factor was found using the fatigue stress concentration factor, which was found with the help of a static stress concentration factor obtained through Finite Element Analysis (FEA). The static stress concentration factor corresponding to the pore was obtained by performing FEA on a large plate with the pore on it. This study focuses on numerical evaluation of the effect of change in the size of the pores of an AlSi10Mg sample on the S–N curve. This method has a high potential to be used as a basis to predict S–N curves for AM components and may be expanded to the components manufactured by other technologies.