The existing literature on study time allocation has primarily focused on how people regulate their study time allocation across different items and conditions. However, these studies rarely investigated how self-regulated study time allocation affects later retention. In this review, the effectiveness of self-regulated study time allocation on retention is evaluated by (1) comparing people who regulated their study time allocation to those who did not and (2) examining whether people reduce or eliminate item difficulty effects through study time allocation. The results suggest that although people benefit from self-pacing their study and selecting what to study, they cannot regulate their study strategies effectively or fully compensate for item difficulty effects through self-regulated study time allocation. Existing theoretical models of study time allocation are discussed in light of these findings, and two alternative theoretical explanations are proposed to account for the findings.