Objective: Problematic alcohol involvement in college students remains a public health concern and identifying factors that promote this consequential behavior as it occurs in daily life is critical. Recent work has found that whether a drinking event is unplanned vs. planned has implications for the risk of negative consequences, though less work has identified fine-grained predictors of these two types of drinking occasions. Method: The present study examined drinking motives and positive and negative affect as predictors of unplanned vs. planned drinking in a sample of college students who completed 28 days of ecological momentary assessment (N = 96; 72% White; 52% female). We examined drinking motives reported at two points: (1) in real-time upon initiating drinking and (2) after one day of retrospection (collected at the daily diary report assessing the prior day). Positive and negative affect were both assessed in real-time. Generalized linear mixed-effects models disentangling within- and between-person effects were leveraged. Results: Drinking “to get high, buzzed, or drunk” — when retrospectively reported for prior-day drinking — exhibited within-person associations with planned drinking, relative to unplanned drinking. This same effect was marginally significant when ascertained in real-time. Individuals with more frequent retrospective endorsement of the motive “to make the day/night more fun” reported more planned drinking. Higher real-time positive affect, but not negative affect, was marginally associated with planned drinking. Conclusions: Our findings provide preliminary support that enhancement motives and higher positive affect are related to planned drinking, which may inform the development of momentary interventions.