Although additively manufactured β-type titanium alloys are attracting increasing interest in implant applications due to their excellent properties, fatigue behavior has so far been insufficiently understood. This is where the present study comes in by experimentally testing and numerically evaluating the direction-dependent cyclic behavior of β Ti-42Nb processed by laser powder bed fusion. Overall, the results highlight the potential for prospective clinical use, but the fracture surface analyses also indicate the importance of defects. In particular, a cavity type that has received little attention to date is identified, whose criticality is higher than that of gas pores. Furthermore, a Pearson correlation analysis reveals that the strain per cycle and the cavity position are more strongly related to the fatigue life than the cavity size and the proportion of crystallographic facets. Finally, a data-driven calculation scheme for nondestructive fatigue limit prediction based on computed tomography data of the cavity population is proposed, which accounts for the size-, position- and shape-dependent criticality of defects. Given comparatively small deviations of 0.4% to 2.7% from the experimental results, this phenomenological approach can become a valuable tool for research and engineering.