<p>Previous research on the Joy of Missing Out (JOMO) remains limited, particularly regarding the availability of measurement instruments that are culturally and contextually appropriate for Indonesia. Therefore, this study aimed to examine the reliability and construct validity of the JOMO instrument among university students. A two-phase exploratory sequential mixed methods design was employed. The first phase involved qualitative exploration with ten undergraduates, which identified three JOMO dimensions: mindful disconnection, joyful disconnection, and digital solitude. In the second phase, reliability estimates indicated high internal consistency (Cronbach’s α = 0.879; McDonald’s ω = 0.878). Exploratory factor analysis revealed a three-factor structure, while confirmatory factor analysis confirmed adequate model fit (CFI = 0.938, TLI = 0.907, RMSEA = 0.081, SRMR = 0.044). To further strengthen psychometric evidence, an Item Response Theory (IRT) analysis using the Partial Credit Model was conducted. Results demonstrated satisfactory person reliability (0.806), acceptable fit statistics for all items (MNSQ 0.8–1.3), and a well-functioning eight-item scale, with difficulty parameters indicating sensitivity to low-to-moderate JOMO levels. Collectively, these findings establish the JOMO scale as a valid and reliable measure of voluntary digital disengagement, offering practical utility for digital well-being research and intervention development.</p>