OBJECTIVES: Randomized controlled trials have shown that Advagraf®, a once-daily prolonged-release tacrolimus formulation, is non-inferior to Prograf®, a twice-daily immediate-release tacrolimus formulation, in terms of biopsy-proven acute rejection in renal transplant recipients. However, relative to Prograf, Advagraf exhibits reduced variability in tacrolimus trough concentration, which has been associated with reduced graft failure. Based on these data, the present study evaluated the cost of switching UK renal transplant patients from Prograf to Advagraf. METHODS: UK-specific data on acute rejection, graft failure and mortality were used to construct a budget impact model to assess the costs of switching from Prograf to Advagraf on a 1:1 mg:mg basis. The model assumed that 3.1% of patients on Advagraf had high tacrolimus trough concentration variability compared with 17.4% on Prograf, based on a study comparing Advagraf and Prograf pharmacokinetics. The model applied a relative risk of graft failure of 2.38 to high variability patients based on data from a tacrolimus variability study. Cost data were taken primarily from the British National Formulary and 2012–13 NHS tariff information and the analysis was performed over a 5-year time horizon. RESULTS: The mean cost per patient (including tacrolimus, concomitant immunosuppressive medications, dialysis after graft failure, and treatment for acute rejection) was GBP 26,958 with Advagraf versus GBP 30,379 for Prograf over a 5-year period. The total cost saving (GBP 3,421) was driven by reduced Advagraf pharmacy costs and lower dialysis costs resulting from the lower proportion of patients with high variability in tacrolimus trough concentrations in the Advagraf arm, leading to lower risk of graft failure. CONCLUSIONS: Converting renal transplant recipients from Prograf to Advagraf was associated with lower pharmacy and dialysis costs, with the reduction in dialysis costs being driven by the lower proportion of Advagraf patients with high tacrolimus trough concentration variability and the resultant improvement in graft survival.