The 24-week EMAX trial in symptomatic patients with chronic obstructive pulmonary disease (COPD) and low exacerbation risk not receiving inhaled corticosteroids demonstrated clinical benefits of once-daily umeclidinium/vilanterol (UMEC/VI) 62.5/25 mcg versus once-daily UMEC 62.5 mcg and twice-daily salmeterol (SAL) 50 mcg. This post hoc analysis assessed cost-effectiveness of UMEC/VI versus UMEC or SAL from a UK payer perspective in patients with COPD and no exacerbation history in the EMAX trial. The validated GALAXY risk equation model was populated with EMAX patient characteristics, treatment effects, rescue medication use data, and 2020 UK costs. Treatment effects included forced expiratory volume in 1 second (FEV1) and St George’s Respiratory Questionnaire (SGRQ); no treatment effect was included for exacerbations. Model outputs included estimated exacerbation rates, survival, costs, life years (LYs), and quality-adjusted LYs (QALYs); incremental cost-effectiveness ratio (ICER) was calculated for cost per QALY gained. The base case used a 10-year time horizon, excluded treatment discontinuation, and discounted future costs and QALYs by 3.5% annually. Sensitivity and scenario analyses assessed robustness of model results. Despite greater incremental drug costs, UMEC/VI was the dominant treatment versus UMEC and SAL, providing an additional 0.090 LYs (95% CI: 0.035, 0.158) and 0.055 QALYs (-0.059, 0.168) with cost savings of £690 (-£1306, -£231) versus UMEC, and 0.174 LYs (0.076, 0.286) and 0.204 QALYs (0.079, 0.326) with cost savings of £1336 (-£2032, -£1006) versus SAL. In scenario and sensitivity analyses, ICERs for UMEC/VI versus UMEC were sensitive to time horizon (5 years: ICER=£4) and SGRQ treatment effect (upper CI: ICER=£12,337), while UMEC/VI was consistently dominant versus SAL. Based on model predictions from a UK NHS perspective, symptomatic patients with COPD and no exacerbation history receiving UMEC/VI are expected to have better outcomes (QALYs and survival) at lower costs versus UMEC and SAL. FUNDING: GSK (study 209845; EMAX study 201749/NCT03034915).