Understanding the relationship between subjective and objective sleep measures is essential for evaluating their agreement and utility. This study compared Munich Chronotype Questionnaire (MCTQ) and Fitbit metrics for sleep duration, sleep midpoint and social jetlag in 5252 participants from the Adolescent Brain Cognitive Development (ABCD) study. Linear and nonlinear models assessed relationships between Fitbit-derived and MCTQ-reported metrics, whilst moderation analyses examined the influence of age, sex, household income and BMI. A sensitivity analysis compared results pre- and post-COVID-19 to assess pandemic-related effects (pre-COVID n = 4451). Correlations were weak to moderate: r = 0.15-0.21 for sleep duration, r = 0.37-0.42 for sleep midpoint, and r = 0.12-0.16 for social jetlag. Quadratic and LOESS models confirmed nonlinear trends for sleep midpoint, with greater Fitbit-MCTQ divergence at extreme morningness or eveningness. Fitbit classified 63.2% of participants as having insufficient sleep, compared to 39.45% with MCTQ, suggesting Fitbit underestimates sleep duration. Bland-Altman plots confirmed MCTQ overestimation, especially for shorter sleepers. BMI was significantly associated with sleep duration and social jetlag, with higher BMI linked to shorter sleep and greater variability. Household income and BMI moderated specific sleep metrics, whilst age and sex did not significantly moderate any metric. Sensitivity analyses showed consistent results across pre- and post-COVID periods. Findings highlight stronger agreement for sleep midpoint than for sleep duration or social jetlag, with methodological differences driving discrepancies. The consistency across demographics and time periods supports the complementary use of Fitbit and MCTQ for adolescent sleep assessment.
