Research on the investment model has assumed that the strength of satisfaction, alternatives, and investments as predictors of commitment vary minimally across individuals or contexts. The present research integrates the investment model with self-determination theory, proposing that motivation moderates the antecedents of commitment. Study 1 tests these hypotheses by separately and meta-analytically analyzing results of 8 independent samples (N = 1,910), in which participants reported on their relationship satisfaction, alternatives, investments, and commitment, along with self-determined relationship motivation. Study 2 employs a weekly diary of students in relationships (N = 121) to test whether baseline self-determined relationship motivation moderates weekly fluctuations in the investment model. Together, results supported hypotheses such that when self-determined relationship motivation was high, alternatives and investments were weaker predictors of commitment. These findings provide novel insight for both the investment model and self-determination theory by advancing our understanding regarding the role of motivation in maintaining commitment.