There is a large literature on the influence of institutional characteristics on student academic achievement. In contrast, relatively little research focusses on student time allocation and its effects on student performance. This paper contributes to the literature by investigating the effect of student time allocation on the average grade of undergraduate students, by gender, ability, and field of study. The results suggest that the time spent on attending courses is positively associated with grades for females, high-ability students, and students of Social Sciences and Sciences/Engineering. Spending time on self-study, on other study-related activities, or on working as a student assistant or tutor is positively correlated with grades for almost all students. Devoting time for attending tutorials or student work groups is negatively correlated with grades if the ability of students is below average or if they study Sciences/Engineering. Using a translog production function, the results indicate that spending time on courses, on self-study, and on other study-related activities are substitutes. However, time spent on courses and time spent on working as a student assistant or tutor are complements.