OBJECTIVES: Advagraf® is a once-daily prolonged-release formulation of tacrolimus with proven non-inferiority to Prograf®, a twice-daily immediate-release formulation of tacrolimus, in biopsy-proven acute rejection in renal transplant recipients. Advagraf is associated with improved adherence compared with Prograf, which may ultimately improve long-term outcomes. The present study assessed the budget impact of switching patients from Prograf to Advagraf in the UK. METHODS: A budget impact model was constructed based on published data on acute rejection, graft failure and mortality in the UK setting. Patients were assumed to convert from Prograf to Advagraf on a 1:1 mg:mg basis. In a study comparing the adherence rates between once-daily versus twice-daily formulations of tacrolimus, the proportion of patients taking the prescribed number of daily doses was 88.2% in Advagraf patients and 78.8% in Prograf patients. The model applied a relative risk of graft failure of 3.47 to non-adherent patients based on data from a 2004 meta-analysis. Cost data were taken from the British National Formulary and 2012–13 NHS tariff information.  The analysis was performed over a 5-year time horizon and future costs were not discounted, in line with International Society for Pharmacoeconomic and Outcomes Research guidelines. RESULTS: Over a 5-year time horizon, the mean cost per patient (including tacrolimus, concomitant immunosuppressive medications, dialysis after graft failure, and treatment for acute rejection) was GBP 29,290 for Advagraf versus GBP 33,032 for Prograf.  The total cost saving of GBP 3,742 was driven by reduced Advagraf pharmacy costs and lower dialysis costs arising from the lower risk of graft failure in the larger proportion of adherent patients in the Advagraf arm. CONCLUSIONS: Conversion of renal transplant recipients from Prograf to Advagraf was associated with lower pharmacy and dialysis costs, with the reduction in dialysis costs being driven by improved adherence to Advagraf regimen and the consequent improvement in graft survival.