Spain's Double-Decker Wealth Tax: The Regional and National Solidarity Tax Dynamic
Spain represents a unique European case study where wealth taxation is organized as a contentious "double-decker" system. This structure is characterized by an ongoing constitutional and political battle between autonomous regions (like Madrid and Andalusia) and the central government. In addition to its political friction, Spain's wealth tax provides critical empirical evidence on subnational tax competition, capital flight, and the broader fiscal impact of wealth taxes on other tax bases.
The Regional vs. National Dynamic
Under Spain’s decentralized tax system, the wealth tax (Impuesto sobre el Patrimonio) is a national tax, but its administration and revenues are devolved to the 17 autonomous regions. This devolution allows regions to set their own tax rates, brackets, and exemptions.
- The Madrid Tax Haven: For years, the Community of Madrid used this power to offer a 100% tax rebate, effectively zeroing out the wealth tax for its residents. This policy attracted thousands of high-net-worth individuals from other parts of Spain, triggering accusations of tax dumping and subnational tax competition.
- The National Counter-Response: To counter this, the central Spanish government introduced the Solidarity Tax on Great Fortunes (Impuesto Temporal de Solidaridad de las Grandes Fortunas) in late 2022. This national tax targets individuals with net wealth exceeding €3 million and operates as a "floor." It allows taxpayers to deduct whatever they pay under their regional wealth tax, effectively neutralizing the 100% tax rebate in Madrid by forcing residents to pay the national government instead.
Empirical Evidence on Mobility: The 2025 AEJ Study
A landmark peer-reviewed study published in the American Economic Journal: Applied Economics (January 2025) by economists David R. Agrawal, Dirk Foremny, and Clara Martínez-Toledano, titled "Wealth Tax Mobility and Tax Coordination", provides a rigorous quantitative evaluation of Spain's wealth tax experiment.
Using administrative tax data, the authors analyzed the mobility responses of wealthy Spaniards to Madrid's 100% wealth tax rebate and the resulting fiscal externalities.
Key Findings:
- Significant Migration Responses: The study confirmed that Madrid's wealth tax exemption led to a substantial inflow of high-net-worth individuals from other Spanish regions. The regional wealth tax differential acted as a powerful driver of subnational tax migration.
- Severe Fiscal Externalities on the Income Tax Base: Crucially, the authors found that when Madrid zeroed out its wealth tax, the regions that lost residents to Madrid suffered a massive fiscal blow that far exceeded the wealth tax itself:
"...regions that lost residents who had moved to Madrid lost six times more personal income tax revenue from each departing taxpayer than they gained in wealth tax revenue."
- The Multiplier Effect of Capital Flight: This finding highlights a major structural hazard of wealth taxes: because wealthy individuals contribute disproportionately to personal income, capital gains, dividend, and consumption taxes, their out-migration in response to a wealth tax erodes the broader, more lucrative tax bases of the jurisdiction they leave behind.
The Solidarity Tax Underperformance
In practice, the national Solidarity Tax has also faced administrative and revenue challenges. According to policy analyses by the Cato Institute and the Tax Foundation in 2026, the Solidarity Tax has suffered from disappointing revenue collections, raising only about 40% of its originally projected revenue.
Furthermore, the tax has induced international tax competition: following the introduction of Spain's Solidarity Tax, neighboring Portugal extended its tax regime for nonresidents to actively recruit Spanish taxpayers who were considering changing their tax residence to avoid the new national levy.