The implementation of the Global Minimum Tax (GMT) represents one of the most fundamental structural overhauls in the history of modern international corporate taxation. Established under the landmark multilateral agreement reached in October 2021 by the OECD/G20 Inclusive Framework, the framework mandates that large multinational enterprises (MNEs) generating annual consolidated revenues of 750 million euros or more must pay an Effective Tax Rate (ETR) of at least 15% on excess profits in every operating jurisdiction. Following years of theoretical modelling and ex-ante forecasts, OECD Working Paper No. 77 authored by Lucía Contreras, Felix Hugger, and Tom Zawisza provides the very first empirical ex-post assessment utilizing realized financial data from the initial implementation year (2024).

The empirical findings presented in the study offer critical insights for tax policy and economic governance. During the first year of GMT implementation, in-scope multinational enterprises experienced a statistically significant increase in their consolidated ETRs ranging between 1 and 2 percentage points. Looking closely at firm-level exposure, MNEs that maintained relatively low effective tax rates prior to the reform recorded an average ETR increase of 1.7 percentage points. When evaluating the entire population of MNEs within the scope of the threshold, the av...