In its Communication on Business Taxation in the 21st Century, the European Commission emphasises the need for a sound, efficient and fair tax framework that meets public financing needs while supporting recovery, sustainable growth and investment. In this context, corporate tax systems and their complexity play an important role in the investment decisions of domestic and foreign companies.

Given the rapid pace of change in taxation, it is important to have the tools and data to analyse the evolution of corporate tax systems and their impact on business decisions. Comparable time series data on the evolution of effective tax burdens are essential as they can inform the policy debate on the impact of corporate taxation. In addition, the data allow the analysis of potential distortions from taxation.

The decision effects of taxation always refer to the future tax burden associated with a particular business decision. Forward-looking tax rates reflect the decision-related tax burden and are therefore best suited for analysing the decision and incentive effects of corporate taxation. In contrast, backward-looking tax rates are always based on empirically observed data, i.e. they do not capture the incentive effects of tax provisions, but reflect the tax consequences of actual business decisions (including tax optimisation and the use of tax incentives). Backward-looking effective tax rates can be derived from company data (unconsolidated or consolidated accounts) or from macroeconomic data.

The project includes a comprehensive review of the literature on backward-looking effective tax rates, the joint development of a common methodology for calculating backward-looking indicators of the effective level of corporate taxation with the EU Commission and the OECD, and the creation of a database of backward-looking effective tax rates, complemented by detailed annual reports.