AbstractObjectivesCognitive stimulation therapy (CST) is one of the few non‐pharmacological interventions for people living with dementia shown to be effective and cost‐effective. What are the current and future cost and health‐related quality of life implications of scaling‐up CST to eligible new cases of dementia in England?Methods/designData from trials were combined with microsimulation and macrosimulation modelling to project future prevalence, needs and costs. Health and social costs, unpaid care costs and quality‐adjusted life years (QALYs) were compared with and without scaling‐up of CST and follow‐on maintenance CST (MCST).ResultsScaling‐up group CST requires year‐on‐year increases in expenditure (mainly on staff), but these would be partially offset by reductions in health and care costs. Unpaid care costs would increase. Scaling‐up MCST would also require additional expenditure, but without generating savings elsewhere. There would be improvements in general cognitive functioning and health‐related quality of life, summarised in terms of QALY gains. Cost per QALY for CST alone would increase from £12,596 in 2015 to £19,573 by 2040, which is below the threshold for cost‐effectiveness used by the National Institute for Health and Care Excellence (NICE). Cost per QALY for CST and MCST combined would grow from £19,883 in 2015 to £30,906 by 2040, making it less likely to be recommended by NICE on cost‐effectiveness grounds.ConclusionsScaling‐up CST England for people with incident dementia can improve lives in an affordable, cost‐effective manner. Adding MCST also improves health‐related quality of life, but the economic evidence is less compelling.