Background <p>Optimal experience (flow) in academic study has been positively associated with student well-being; however, the precise day-to-day temporal ordering of this relationship remains to be empirically clarified. To advance this understanding, the present study examined within-person reciprocal associations between academic flow and subjective well-being among university students.</p> Methods <p>A 21-day daily diary design was employed with 51 university students, yielding 1,006 valid daily observations and a compliance rate of 93.9%. Subjective well-being was assessed across three dimensions: positive affect, negative affect, and life satisfaction. Three Bayesian dynamic structural equation models were estimated to capture within-person dynamics, with daily sleep duration incorporated as a control variable.</p> Results <p>Significant within-person autoregressive effects were identified for all study variables. Daily academic flow prospectively predicted positive affect and life satisfaction on the following day, whereas neither well-being component predicted subsequent flow, indicating a unidirectional rather than reciprocal association. No longitudinal association was observed between flow and negative affect.</p> Conclusions <p>These findings support the temporal precedence of academic flow in predicting daily subjective well-being, consistent with a eudaimonic perspective on student development. In practice, these results encourage educators and institutional practitioners to prioritize cultivating optimal learning experiences as a meaningful strategy to sustain student well-being in higher education.</p>