The wellbeing-adjusted life year (WELBY) is a single metric that shows the impacts of policies and interventions on life expectancy and individual wellbeing. In contrast to the quality-adjusted life year (QALY) that is currently widely-used in health economic evaluation, the WELBY is based on subjective wellbeing for each individual. In this talk, Lord O’Donnell will discuss the rationale for using subjective wellbeing to guide policy, the methodologies used for calculating WELBYs and how their use would change the priorities of policy-makers compared to GDP or QALY targeting. He will also use his experience of guiding policy inside and outside government to discuss the barriers to implementing policies that target wellbeing, and the opportunities for research to change that.