This study focuses on the numerical simulation of short crack growth to investigate geometric interaction effects between small neighboring defects under consideration of crack closure. In an extensive parameter study, circular cracks of various sizes and interaction distances are investigated. The simulation procedure follows a cyclic R-curve analysis in order to determine the fatigue limit of maximum non-propagating crack formation. The interaction effects are quantified in the form of novel geometry factors for interacting cracks as well as the degradation of the fatigue limit due to crack size and proximity. The results are compared to experimental validation tests performed on additively manufactured specimens containing artificial defects.