Government revenues may be affected by economic growth and changes in demographics over time. The effect of economic growth can be captured by long-run buoyancy – responsiveness of government revenues to GDP growth – while the demographic effect can be captured by changes in labour income, asset income and consumption patterns over the life cycle, as well as population growth. This paper attempts to quantify the effect of population ageing on OECD tax revenues across different levels of government, by estimating error correction models of revenue buoyancies over the 1990 to 2018 period, by type of revenue, country and level of government. Multiple scenarios are used for the projections to 2040, which are combined with scenarios for the evolution of revenue bases using newly harmonized EU and UN National Transfer Accounts data as well as OECD Population Projections.