The use of fitness apps (some based on behavior change theories) is increasing. Recently a taxonomy mapped app features to the Basic Psychological Needs (BPNs) posited by the Self-Determination The- ory (SDT), providing the opportunity to inform the design of fitness apps by this theory of human motivation. However, it is unknown if the user’s perceptions of such SDT-based design would support the BPNs. This is important as the SDT states that interventions supporting the BPNs produce long-term benefits. Following the taxonomy of app features based on SDT, we designed and developed Agon, an iPhone app. We deployed the app through a one-month field study involving 49 participants. The study allowed participants to use the app in their everyday lives, providing sufficient exposure for us to capture meaningful perceptions. This work contributes empirical evidence that the features included in our design correctly mapped to the Basic Psychological Needs. We discuss implications for researchers and designers targeting effective interventions.