Background <p>The rapid increase in smartphone usage among university students has raised concerns about problematic use and its implications for mental well-being. While most existing studies adopt psychological perspectives, limited research interprets excessive smartphone use through an economic lens. Drawing on theories of rational addiction and time allocation, excessive smartphone use can be conceptualized as a form of utility-reducing consumption, where time spent on smartphones displaces welfare-enhancing activities such as physical activity and social interaction. This study aims to examine the determinants of smartphone addiction within a behavioral economic framework, focusing on its association with mental well-being and time-use-related behaviors among university students in Bangladesh.</p> Methods <p>A cross-sectional study was conducted among 500 university students in Bangladesh using a structured online questionnaire. Smartphone addiction risk was measured using the Smartphone Addiction Scale–Short Version (SAS-SV), while mental well-being and self-esteem were assessed using the WHO-5 and Rosenberg Self-Esteem Scale. Binary logistic regression models were estimated to identify factors associated with high-risk smartphone addiction.</p> Results <p>Approximately 54% of respondents were classified as high risk for smartphone addiction. Low mental well-being was significantly associated with higher odds of smartphone addiction (OR = 1.99, 95% CI: 1.14–4.79).</p> Conclusion <p>The findings suggest that smartphone addiction can be interpreted as a utility-reducing behavior associated with diminished mental well-being within a time allocation framework. Behavioral factors appear more relevant than demographic characteristics in explaining problematic smartphone use. However, due to the cross-sectional design, causal relationships cannot be established.</p>