Dual bronchodilators are recommended as maintenance treatment for patients with symptomatic COPD in the UK; further evidence is needed to evaluate cost-effectiveness versus monotherapy. Cost-effectiveness of umeclidinium/vilanterol versus umeclidinium and salmeterol from a UK healthcare perspective in patients without exacerbations in the previous year was assessed using post hoc EMAX trial data. The validated GALAXY model was populated with baseline characteristics and treatment effects from the non-exacerbating subgroup of the symptomatic EMAX population (COPD assessment test score ≥10) and 2020 UK healthcare and drug costs. Outputs included estimated exacerbation rates, costs, life-years (LYs), and quality-adjusted LYs (QALYs); incremental cost-effectiveness ratio (ICER) was calculated as incremental cost/QALY gained. The base case (probabilistic model) used a 10-year time horizon, assumed no treatment discontinuation, and discounted future costs and QALYs by 3.5% annually. Sensitivity and scenario analyses assessed robustness of model results. Umeclidinium/vilanterol treatment was dominant versus umeclidinium and salmeterol, providing an additional 0.090 LYs (95% range: 0.035, 0.158) and 0.055 QALYs (-0.059, 0.168) with total cost savings of £690 (£231, £1306) versus umeclidinium, and 0.174 LYs (0.076, 0.286) and 0.204 QALYs (0.079, 0.326) with savings of £1336 (£1006, £2032) versus salmeterol. In scenario and sensitivity analyses, umeclidinium/vilanterol was dominant versus umeclidinium except over a 5-year time horizon (more QALYs at higher total cost; ICER=£4/QALY gained) and at the lowest estimate of the St George's Respiratory Questionnaire treatment effect (fewer QALYs at lower total cost; ICER=£12,284/QALY gained); umeclidinium/vilanterol was consistently dominant versus salmeterol. At willingness-to-pay threshold of £20,000/QALY, probability that umeclidinium/vilanterol was cost-effective in this non-exacerbating subgroup was 95% versus umeclidinium and 100% versus salmeterol. Based on model predictions from a UK perspective, symptomatic patients with COPD and no exacerbations in the prior year receiving umeclidinium/vilanterol are expected to have better outcomes at lower costs versus umeclidinium and salmeterol.