Objective: Unplanned drinking, or drinking that violates intentions to limit alcohol consumption, has been linked to significant alcohol-related consequences in college students; however, predictors and outcomes remain incompletely understood among other populations of young adults. This study identified person- and event-level predictors of unplanned drinking and explore the association of unplanned drinking with negative alcohol-related consequences in a racially and educationally diverse cohort of young adults., Method: A total of 938 young adults (aged 18-25; 70 % female; 60 % non-college; 37 % Black) participating in a randomized trial testing text-message alcohol interventions completed ecological momentary assessments (EMA) reporting drinking intentions and alcohol consumption twice weekly for at least 4 weeks over a 14 week period. Controlling for intervention effects, mixed-effects models examined predictors of unplanned drinking days, and zero-inflated negative binomial regression models assessed the relationship between frequency of unplanned drinking and negative alcohol consequences at a 14-week follow-up., Results: Participants reported alcohol consumption on 16.9 % of days when they had no plan to drink. Odds of unplanned drinking was higher for older age (adjusted Odds Ratio [aOR] = 1.06, p < 0.01), Black race (aOR = 1.25, p < 0.01), higher AUDIT-C score (aOR = 1.14, p < 0.001), and higher negative urgency score (aOR = 1.05, p < 0.01), weekends (aOR = 1.63, p < 0.001) and the presence of friends drinking (aOR = 9.37, p < 0.001). Compared to participants in the lowest unplanned drinking day category, those in the highest category showed a 26 % higher negative alcohol consequence rate ratio (RR = 1.26, 95 % CI [1.07, 1.48])., Conclusions: Unplanned drinking in young adults is strongly influenced by social context and individual risk factors. This behavior, when extreme, was associated with increased negative alcohol-related consequences. Interventions targeting impulsivity and peer influence may reduce unplanned drinking and mitigate its harmful effects., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2025 Elsevier Ltd. All rights reserved.)