 This retrospective cohort study investigates the characteristics of adherence to using the NoMAP for weight loss and compares the effects of using the app on body weight changes over time according to adherence to the use of the app between users in low-income and OECD countries. The results suggest that using the app has a significant effect on weight loss regardless of users' country of residence and the frequency of monitoring health-related behaviors by entering data into the app plays a pivotal role in losing weight. This article was authored by Myung-hee Han and sang Yul Ri.