Fitness trackers are increasingly used by their wearers to monitor and optimise their exercise, health, and well-being. What is usually not considered is the role our interoceptive sense, the sense for inner-bodily processes, plays in the interpretation of body data and the formation of habits. By including neuroscientific research, perspectives from pragmatist philosophy, and science and technology studies into the analysis of self-tracking devices, this article will give a perspective on the scope and the effects of the involvement of the interoceptive sense in self-tracking practices. By offering a critical analysis of the contextualisation of experience through self-tracking devices, this article will argue that interoceptive awareness provides the context to make sense of body data. I propose here that paying greater attention to how interoception is involved in the mediation of bodily processes and activities through tracking devices can give novel insights into self-tracking as an embodied and affective practice.