The article presents an experimental and numerical analysis of the influence of the hole chamfer size of a single lap joint with a blind rivet on contact stresses. The rivet–hole interface is critical due to the presence of secondary bending, stress concentration, shear stress, and local plastic deformation. To better understand the deformation and failure mechanisms, cross-sectional views of riveted joints under different loads were examined. Contact stresses were also analyzed using the classical Hertzian model, which, while useful under idealized conditions, fails to account for complex geometry and material nonlinearity. A modified version of the Hertz model was therefore proposed, incorporating geometric corrections based on the chamfer size and angle. The research object is a single-lap riveted joint made by the ISO 12996 standard, modelled using a discrete riveted model and nonlinear material properties. Different hole chamfer size configurations and various load cases were considered in the analyses to better illustrate the relationship between the numerical and experimental results. Contact stresses and stress distribution in the riveted joint cross-section were analysed. Results showed that increasing the chamfer depth significantly affects the distribution of contact stresses and improves rivet forming and load capacity, although it also increases the risk of localized overloading. A strong qualitative agreement was found among experimental data, numerical analysis, and the modified analytical model. The research demonstrates the effectiveness of a hybrid analytical - numerical approach for accurately evaluating stress behavior in riveted joints under complex loading conditions.