Spain's Large Fortunes Tax: Structural Friction with Double Taxation Treaties

Spain's Solidarity Tax on Large Fortunes (ITSGF), introduced in late 2022, is no longer a temporary measure. Its continued application, extended indefinitely and validated by the Constitutional Court, cements it as a structural component of the Spanish tax system. This shift in status moves the focus from short-term mitigation to long-term wealth planning. The central question is no longer whether the tax will persist, but how to manage the conflict it creates with the protections of double taxation treaties (DTTs), a direct challenge for non-residents with assets in Spain.

From Temporary Measure to Fiscal Pillar

The ITSGF was introduced by Law 38/2022, initially designed for the 2022 and 2023 fiscal years. Its purpose was twofold: revenue generation and harmonization. It functions as a state-level net wealth tax that supplements the traditional Wealth Tax (Impuesto sobre el Patrimonio, IP), which is managed by Spain's Autonomous Communities. In practice, the ITSGF is triggered in regions that have granted full or partial relief on their local IP, such as Madrid or Andalusia, thereby ensuring a minimum national tax burden. The taxpayer settles the higher of the two tax liabilities, preventing internal double taxation.

The tax base is the worldwide net worth for Spanish tax residents and assets located in Spain for non-residents, with an exemption threshold of EUR 3,000,000. Rates are progressive, ranging from 1.7% to a top rate of 3.5% for net wealth exceeding EUR 10,695,996.06. A key development was its indefinite extension through legislation enacted in late 2023, pending a future review of the regional financing system. However, the turning point was the jurisprudence of the Constitutional Court, which in late 2023 dismissed challenges to the tax's constitutionality. By validating the state's authority to create the tax, the Court removed the primary legal uncertainty and transformed the ITSGF into a fiscal certainty for wealth planning purposes.

Conflict with Double Taxation Treaties

The consolidation of the ITSGF as a permanent wealth tax sharpens its friction with Spain's network of DTTs. Many of these treaties, particularly those based on pre-1990s OECD models, were focused on income and only marginally on capital. The controversy centers on whether a comprehensive net wealth tax like the ITSGF fits within the definition of "taxes on capital" covered by Article 22 of the OECD Model Tax Convention.

The ITSGF is levied not on a specific capital asset or its yield, but on net wealth as a whole. In older DTTs that do not contemplate such a tax, Spain's Directorate-General for Taxation (DGT) may argue that the tax falls outside the treaty's scope, allowing Spain to tax non-residents without treaty limitations. Even in more modern treaties that do cover wealth taxes, the clauses typically assign taxing rights to the taxpayer's jurisdiction of residence for most assets, with the notable exception of real estate, which is taxed where it is situated.

The treatment of indirect structures magnifies the problem. A common strategy for non-residents has been to hold Spanish real estate through a non-resident entity. The objective was for the asset subject to Spanish taxation to be the shares in the foreign company, not the property itself, with the taxing rights over those shares allocated by the DTT to the shareholder's country of residence. However, Spanish domestic law contains "look-through" provisions. These rules allow the Spanish Tax Agency to tax the non-resident on their shares in the foreign entity if more than 50% of its assets consist, directly or indirectly, of real estate located in Spain. This application of domestic law clashes with the allocation of taxing rights in many DTTs, creating considerable legal uncertainty. Jurisdictions like France and Norway have faced similar debates, but Spain's fiscal stance on the application of its domestic rules creates particular uncertainty for investors.

Structural Implications

The permanence of the ITSGF demands a strategic reassessment from any estate with a nexus to Spain. The consequences differ for residents and non-residents, but for both, a reactive approach to planning is no longer sustainable.

For Spanish tax residents, the combined effect of the ITSGF and regional IP can result in an annual tax burden that significantly erodes capital returns. This reality has intensified the analysis of relocating tax residence to jurisdictions with more favorable regimes. Destinations such as Italy (with its imposta sostitutiva), the UK (despite recent reforms to its "non-dom" regime), and the United Arab Emirates are solidifying as strategic alternatives to a tax charge that has shifted from temporary to structural.

For non-residents, the priority is the holding structure of their Spanish assets. Using foreign companies to own Spanish real estate is now a compromised strategy. Action is required on several fronts. First, a detailed analysis of the applicable DTT is essential to determine if it covers wealth taxes and how it regulates the taxation of shares in real estate-heavy companies. Second, debt structuring is a key factor. The ITSGF is levied on net wealth, so legitimate, arm's-length financing for the acquisition of Spanish assets can reduce the tax base. Third, an accurate and defensible asset valuation is critical to prevent the tax base from being adjusted upwards by the tax authorities. Finally, asset diversification beyond real estate may mitigate risk, although the ITSGF applies to all assets located in Spain, including company shares, bank deposits, and other rights.

The obligation to file Form 718 for non-residents exceeding the threshold increases their administrative burden and visibility to the Tax Agency. Any structure involving Spanish assets must now be designed on the assumption that the ITSGF is a permanent factor and that the tax administration will actively use its powers to challenge structures it deems elusive. The era of passive tax planning for assets in Spain is over.