Current personal informatics models consider reflection as an important stage in users’ journeys with trackers. However, these models describe reflection from a meta perspective and it remains unclear what this stage entails. To design interactive technologies that support reflection, we need a more thorough understanding of how people reflect on their personal data in practice. To that end, we conducted semi-structured interviews with users of fitness trackers and an online survey to study practices in reflecting on fitness data. Our results show that users reported reflecting on data despite lacking reflection support from their tracking technology. Based on our results, we introduce the Technology-Mediated Reflection Model, which describes conditions and barriers for reflection on personal data. Our model consists of the temporal and conceptual cycles of reflection and helps designers identify the possible barriers a user might face when using a system for reflection.