Our paper adds to a growing literature of doctoral training by studying factors that drive time-to-completion based on a new and unique data set from an international European graduate school. While previous research focused on individual factors, we inspect the role of institutional factors and the organization of PhD programs for PhD completion. Based on a theoretical model, we elaborate hypotheses on three sets of institutional factors for thesis submission rates. We use event history analysis to analyze register data on 30 entry cohorts of PhD students. Our findings demonstrate the relevance of the factors related to the institutional environment like the density of supervision and support. Furthermore, our results underscore the importance of program structuration through clear deadlines and sufficient length of funding. We conclude with a discussion on effective measures that can be taken by program designers and grant authorities aiming to improve completion rates in PhD schools.