Since 1995, tax levels and tax structures in OECD countries have converged around a higher average tax-to-GDP ratio and an average tax structure that is more reliant on value-added taxes, social security contributions, and corporate income taxes, while less reliant on personal income taxes and other forms of taxes and goods and services. In 2017, these trends continued, with the OECD average tax-to-GDP ratio continuing its steady increase to a high of 34.2%.
Taxes are defined as compulsory, unrequited payments to general government. They are unrequited in that the benefits provided by governments to taxpayers are not normally allocated in proportion to their payments. Taxes are classified by their base: income, profits and capital gains; payroll; property; goods and services; and other taxes. Compulsory social security contributions (SSCs) paid to general government are also treated as taxes. Revenues are analysed by level of government: federal or central; state; local; and social security funds. Detailed information on the classifications applied is set out in the Interpretative Guide in Annex A.