Self-monitoring is the strongest predictor of success in lifestyle interventions for obesity. In this secondary analysis of the GoalTracker trial, we describe outcomes of consistently self-monitoring in a standalone weight loss intervention. The 12-week intervention focused on daily self-monitoring of diet and/or body weight in a commercial app (MyFitnessPal). Participants (N = 100; 21–65 years; BMI 25–45 kg/m2) were categorized as Consistent Trackers if they tracked ≥ 6 out of 7 days for at least 75% of the targeted weeks. One-fourth of participants were Consistent Trackers. This subset was more likely to be married or living with a partner, be non-Hispanic White, and have higher health literacy than Inconsistent Trackers (ps < .05). Consistent tracking was associated with greater weight change than inconsistent tracking at 1 month (mean difference [95% CI] − 1.11 kg [− 2.12, − 0.10]), 3 months (− 2.42 kg [− 3.80, − 1.04]), and 6 months (− 2.13 kg [− 3.99, − 0.27]). Over 3 times as many Consistent Trackers as Inconsistent Trackers achieved ≥ 5% weight loss at 3 months (48 vs. 13%) and at 6 months (54 vs. 15%; ps < .001). Though causality cannot be determined by the present study, tracking weight and/or diet nearly every day per week for 12 weeks in a commercial app may serve as an effective strategy for weight loss. Strategies are needed to promote greater consistency in tracking.