Emotion regulation variability and flexibility in daily life show distinct associations with well-being, age, and executive functions.

Flexible and effective emotion regulation (ER) is crucial for mental health and well-being. Research on individual differences in ER, however, has often relied on global self-reports or controlled laboratory settings, which may not fully capture the dynamic and context-dependent nature of regulation in daily life. To address this, we examined how ER variability and flexibility in real-world contexts relate to executive functions (EF), affective well-being, and age in a general population sample (N = 161, aged 14-78). EF performance was assessed using six online cognitive tasks, while ER variability and flexibility were assessed using a 14-day ambulatory assessment of daily emotional experiences. As expected, EF performance declined with increasing age across shifting, inhibition, and updating domains. Beyond these age-related differences in cognitive performance, older age was robustly associated with lower within- and between-strategy ER variability. In contrast, ER flexibility remained relatively stable across adulthood. Individual differences in EF were not associated with everyday ER variability, suggesting that cognitive control capacity does not account for regulatory dispersion in daily life. For affective well-being, ER flexibility showed specific, nonlinear associations: within-strategy flexibility based on situational valence and social context demonstrated U-shaped relations with unpleasant mood, suggesting that both low and high context sensitivity may be linked to elevated negative affect. In contrast, flexibility indices were unrelated to between-strategy variability or depressive symptoms. Overall, these findings indicate that adaptive ER cannot be reduced to greater executive control capacity, greater variability, or greater flexibility per se. Instead, they underscore the importance of distinguishing variability from flexibility and highlight that the adaptiveness of ER may depend more on the appropriateness of strategy-context matches than on general patterns of strategy use.