Abstract Purpose To determine: (1) the smallest change in function patients would need to see following a self-management intervention for low back pain (LBP) to consider it worthwhile; (2) the association between patient-related factors and the magnitude of the smallest worthwhile change. Methods A cross-sectional analysis of 212 participants of the TEXT4myBACK randomised trial was conducted. At baseline, participants nominated the smallest change in function (0–30 scale) following a self-management program they would need to reach to consider it worthwhile. A multivariate regression model estimated the effects of demographic, comorbidities, lifestyle and LBP-related factors on the smallest worthwhile change estimates. Results On average, people with LBP need to experience an improvement of at least 9.4 points (SD: 5.7) in function to consider a self-management intervention worthwhile. Only baseline function severity was significantly associated with the smallest worthwhile estimate (−0.60; 95%CI − 0.76, − 0.44). Conclusion On average, an improvement of 9.4 points (or 31%) in function is considered by people with LBP as the smallest change that makes self-management worthwhile. Those with lower levels of function needed to experience greater improvements.