Degree completion on theoretical time is a phenomenon seldom explored in the higher education literature. We applied variance components models and random coefficients models to the microdata of an entire entrant cohort of first-time, full-time undergraduate students who completed their three-year programme at a Portuguese institution during the theoretical period. The study showed that the variance partition coefficient is 0.27, considering the hierarchical structure of students nested in programmes. The differential effect of students' university entrance scores on degree completion grade point average is stronger across programmes than across faculties, controlling for students' sociodemographic background (gender, age and parents' level of education), social scholarship granted, and preference regarding the institution and programme attended. The fixed effects related to the areas of study and type of institution (e.g. university or polytechnic) were also quantified. The estimates indicated that secondary school preparation is the most important predictive factor for the final grade point average of degree completion among the variables at enrolment. Moreover, differences based on gender, age, and areas of study were found.