For many people living with long COVID (PWLC), self-tracking has emerged as a valuable practice to monitor their illness. An examination of self-tracking practices can, therefore, shed light on the ways in which individuals navigate their care, make sense of their experiences and advocate for their needs. This study investigates how PWLC engage in self-tracking practices and how they utilise and negotiate the data generated. Based on 33 semi-structured interviews with PWLC in the Netherlands, Austria and Switzerland, we found that PWLC use self-tracking to recognise patterns and identify limits, triggers and effective interventions. The insights drawn from this are used to make informed decisions about health management strategies. Yet, self-tracking may also reify symptoms and negatively influence the subjective illness experience, exacerbating stress and anxiety. Although PWLC themselves negotiate and question their tracking data, they find a variety of responses from healthcare providers in clinical interactions. Using the concept of 'trading zone' (Kjærulff and Langstrup), we argue that although self-tracking cannot replace treatment and good care, its integration into the healthcare experience as a valuable form of patient knowledge may improve the patient-provider relationship.