This study examined the role of situational features and betting platforms in harmful betting behaviours and experience of short-term harm. An ecological momentary assessment (EMA) study was conducted. A total of 267 Australians between 18 and 29 years old completed a baseline survey and 10 EMA surveys. Each EMA survey was completed one week apart. The data analyzed included details on 1,378 betting sessions on sports, esports, or daily fantasy sports. The findings revealed five situational features of betting sessions: (1) quick, easy access from home; (2) ability to bet anywhere anytime; (3) privacy while betting; (4) greater access to promotions and betting options; and (5) ability to use electronic financial transactions. Three situational features were associated with greater short-term harm, including privacy when betting, ability to bet anywhere anytime, and greater access to promotions and betting options. Only smartphone betting combined all these three features. Participants with more severe gambling problems were more likely to prioritize two situational features linked to short-term harm: ability to bet anywhere anytime and privacy when betting.