Heavy alcohol use is common among young adults on weekend nights and is assumed to be intentional. However, little is known about the extent to which heavy consumption is planned prior to the onset of drinking and what factors contribute to drinking more than intended. This study investigates drinking intentions at the beginning of an evening and individual and situational factors associated with a subsequent consumption over the course of multiple nights.Using a smartphone application, 176 young people aged 16 to 25 (mean age = 19.1; 49% women) completed questionnaires on drinking intentions, consumption, and drinking environments before, during, and after multiple Friday and Saturday nights (n = 757). Multilevel regressions were used to investigate individual-level and night-level factors associated with previous drinking intentions and subsequent deviations from intentions.Participants intended to consume 2.5 drinks (SD = 2.8) per night yet consumed 3.8 drinks (SD = 3.9) on average. Drinking intentions were higher among those who frequently went out at night and engaged in more frequent predrinking. Participants drank more than intended on 361 nights (47.7%). For both genders, the number of drinks consumed before 8 pm, attending multiple locations, and being with larger groups of friends contributed to higher consumption than intended at the individual and the night levels. Heavier consumption than intended also occurred when drinking away from home for men and when going to nightclubs for women.Making young adults aware of the tendency to drink more than intended, particularly when drinking begins early in the evening, moves from location to location, and includes large groups of friends, may be a fruitful prevention target. Structural measures, including responsible beverage service, may also help in preventing excessive drinking at multiple locations.