Under Brazil’s 2024 G20 presidency, the idea of taxing the ultra-rich gained unprecedented momentum, reflecting a major shift in public and political will. At the Taxing Billionaires’ conference* held at the Paris School of Economics on 8-9 April 2025, economists called for a coalition of the willing countries, spanning the Global South and the Global North, to put issues of tax progressivity, equality, planetary sustainability at the heart of international economic relations. They stressed the importance of grounding these discussions in transparent and democratic processes.
A new tool to support the public debate
On the occasion of the conference, the World Inequality Lab released a new version of the Global Wealth Tax Simulator – an innovative tool designed for researchers, policymakers, and citizens. It now allows users to explore and compare tax scenarios in a consistent framework across all countries. Based on Distributional National Accounts and rich lists, it ensures micro–macro consistency and aims to democratize the debate on the taxation of high-net-worth individuals.
A first version of the Global Wealth Tax simulator was released alongside the World Inequality Report 2022. The new updated version is based on more extensive and comprehensive wealth data. Further updates are in the pipeline, including a global income tax simulator and an updated version of the income and wealth comparator.
Two decades tracking wealth inequality
Over the past two decades, research on inequality and taxation has made significant progress. Using the methodology of Distributional National Accounts (DINA), the World Inequality Lab has expanded the World Inequality Database with new indicators and greater coverage over time and space.
Today, WID wealth inequality data represents approximately three-quarters of global household wealth, with historical data going as far back as 1913 for the United States or 1961 for India, among other countries.
Lucas Chancel, Co-director of the World Inequality Lab, said:
“Two decades tracking wealth inequality helped, partly, escape the dark age of inequality statistics.”
Research shows that wealth is increasingly concentrated at the top. And yet, modern tax systems fall short in effectively taxing the ultra-wealthy.
On the first day of the conference, researchers working on the effective taxation of high-net-worth individuals compared results and methodology. Results from France, the Netherlands, Italy, the United Kingdom, Brazil, the United States, Norway, and Switzerland show strikingly similar trends in billionaire wealth accumulation and low effective tax rates.
“All taxes included, the super-rich pay less tax than other groups, typically around 15-20-25% of their income in tax when the working class, the middle class pay 35-40-50-55%, depending on the country”, said Gabriel Zucman, Co-Director of the EU Tax Observatory.
From research to policy
The results of the research have trickled down into the policy space. Last year, the proposal for a tax on the ultra-high-net-worth individuals was for the first time ever put on a G20 agenda by Gabriel Zucman under the Brazilian Presidency. This initiative built on a key recommendation from the EU Tax Observatory’s Global Tax Evasion Report, which proposed “a minimum wealth tax on billionaires equal to 2% of their wealth, that would generate nearly $250 billion from less than 3,000 individuals”.
Reflecting on this proposal during the conference, Gabriel Zucman said:
“It’s not about creating tax progressivity in our tax system. It is about making sure that there is no regressivity at the very top […] It’s a minimal implementation of a basic principle that’s actually written into the constitutions of many countries.”
Thomas Piketty, Co-Director of the World Inequality Lab, added:
“A 2 % tax on billionaires is a very useful and important first step – but it’s important not to stop there. In the past, many wealth taxes, in France in particular, failed because they were unable to convince public opinion or demonstrate that billionaires were effectively taxed. Building public confidence in the idea that it is truly possible to target the ultra-wealthy -those with over 100 or 200 million, and billionaires in particular – is essential.
We also need broader reforms to address the challenges of the 21st Century. Beyond taxation, there are structural reforms of the international monetary and trade systems that could bring redistribution of greater magnitude than the tax system strictly speaking”.
From India to France, wealth tax proposals are gaining ground. By making wealth taxation scenarios accessible and comparable across countries, the Global Wealth Tax Simulator will empower researchers, policymakers, and citizens alike to engage in the debate.
*The two-day International Conference on Taxing Billionaires was organized by the PSE Stone Center in collaboration with the EU Tax Observatory, the World Inequality Lab, the Institut des Politiques Publiques, and École Normale Supérieure.
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