Abstract Aims This study aims to explore possible associations between self‐efficacy and healthcare and drug expenditures (i.e. direct costs) in patients with chronic heart failure (CHF) or chronic obstructive pulmonary disease (COPD) in a study investigating the effects of person‐centred care delivered by telephone. Methods and results This exploratory analysis uses data from an open randomized controlled trial conducted between January 2015 and November 2016, providing remote person‐centred care by phone to patients with CHF, COPD, or both. Patients hospitalized due to worsening of CHF or COPD were eligible for the study. Randomization was based on a computer‐generated list, stratified for age ≥ 75 and diagnosis. At a 6 month follow‐up, 118 persons remained in a control group and 103 in an intervention group. The intervention group received person‐centred care by phone as an addition to usual care. Trial data were linked to register data on healthcare and drug use. Group‐based trajectory modelling was applied to identify trajectories for general self‐efficacy and direct costs. Next, associations between self‐efficacy trajectories and costs were assessed using regression analysis. Five trajectories were identified for general self‐efficacy, of which three indicated different levels of increasing or stable self‐efficacy, while two showed a decrease over time in self‐efficacy. Three trajectories were identified for costs, indicating a gradient from lower to higher accumulated costs. Increasing or stable self‐efficacy was associated with lower direct costs ( P  = 0.0013). Conclusions The findings show that an increased or sustained self‐efficacy is associated with lower direct costs in patients with CHF or COPD. Person‐centred phone contacts used as an add‐on to usual care could result in lower direct costs for those with stable or increasing self‐efficacy.