BACKGROUND: Dementia represents one of the greatest global health challenges. There are known risk factors that might prevent or delay nearly 50% of the different types of dementia. There are substantial differences in risk factors and progression of dementia between women and men, including engagement in regular physical activity. The study aimed to quantify the impact of increasing women's participation in physical activity with off-road cycles and its effect on dementia incidence, relative to men and the associated health and social care costs. METHODS: Our study employed a population model with secondary data analysis approach to investigate the potential economic effect of implementing off-cycle lanes in the UK. Data were drawn from published evidence on lifetime risk of dementia relative to physical activity in men and women for the UK population, levels of physical activity in the UK, evidence on the effectiveness of off-road cycle lanes in increasing the level of physical activity in men and women, lifetime costs of dementia in the UK. Two scenarios were compared, assuming an increase from the baseline levels of cycling of 40.3% and 114% for women and by 36.4% and 77% for men, respectively. Sensitivity analysis was conducted to account for variations in key variables. RESULTS: Current dementia related lifetime costs were estimated at £1090.1 billion, and total lifetime costs £3326.1 billion. Under Scenario 1, dementia related lifetime costs decreased by £4.7 billion, and total lifetime costs by £0.11 billion. In Scenario 2, dementia related lifetime costs decreased by £7.0 billion, and total lifetime costs by £1.9 billion. CONCLUSION: Off-road cycle lanes, especially for women, this type of structural and lifestyle intervention has the potential to bring health and economic benefits. Increased physical activity not only provides numerous health benefits, but also contributes to preventing the onset and lifetime costs of dementia.