self-reflection is the tendency to reflect on one’s thoughts, feelings, and behaviours. it has a strong foundation in psychology for conferring self-knowledge and self-awareness. journaling is an example of an activity that requires much self-reflection, and as an intervention has positive effects on mood, wellbeing, and the ability to proactively ward off stress. paradoxically, however, self-reflection may also be associated with mental health symptoms, possibly through its relationship with rumination. gaps exist in the literature as to whether self-reflection predicts one’s choice to journal, as well as whether self-reflection affects the extent to which journaling confers benefit. in the current study, participants (n = 152) had access to a smartphone app with various features, including a journal. they were encouraged to use the app throughout a 28-day period, choosing which features to use and for how long, and completed self-report measures at baseline, midpoint, and post-app periods. i hypothesized baseline self-reflection would predict journal usage, and that self-reflection would affect the extent to which journaling was associated with improvement in affect, self-regulation, and psychological wellbeing. unexpectedly, using count regression models, self-reflection did not predict journal usage, though both rumination and keeping a journal outside of the study predicted the choice to journal. multilevel models also revealed that, as expected, time spent journaling was associated with lower negative affect and higher self-regulation and psychological wellbeing over time, though some of these effects were diminished when accounting for time spent using other app features. further, as hypothesized, higher baseline self-reflection was associated with greater improvement in psychological wellbeing the more one journaled, even when controlling for rumination. findings highlight the benefit of journaling to promote wellbeing when self-reflection is high, although those higher in rumination may be more likely to engage in the behaviour to begin with.