BackgroundEmotion regulation (ER) plays an important role for mental health. However, there is limited research involving ER variability as a prerequisite for adaptive ER. The present study assessed the relations between two indicators of ER variability (between- and within-strategy), depressive symptoms, perceived ER effort and success, and age. MethodsWe implemented a three-week ambulatory assessment study during a nationwide lockdown in Germany during the Covid-19 pandemic (April 2020). The sample comprised 322 participants aged between 15 and 82 years (M = 28.8 years, SD = 14.0, 74.5 % female). Participants reported their daily use of ER strategies in the evening. The data were analysed with stepwise regression analyses. ResultsWe found significant positive associations between within-strategy variability and depressive symptoms. Perceived ER effort was positively correlated to depressive symptoms, while perceived ER success was negatively associated with depressive symptoms. Between-strategy variability did not show a significant connection to depressive symptoms. Age was negatively associated with within-strategy variability. ConclusionsThe findings support that day-to-day ER variability, particularly within-strategy variability, is a significant correlate of depressive symptoms across a wide age range. Our results underscore the importance of considering situational context information when analyzing the adaptiveness of specific ER patterns.