This study compared an extended online gambling intervention to a brief online personalized feedback intervention. Both interventions reduced days of gambling and problem gambling severity, but no differences between the two were found. Thus, the extended online intervention was not associated with better outcomes. Self-efficacy increased over time but did not explain changes in gambling. Participants who were most engaged in the extended online intervention showed better outcomes at 3-month follow-up. Participants who were not as engaged had slower changes in gambling, but achieved similar improvements by 12 months.