Moving to Spain or Portugal offers an exceptional lifestyle, but for U.S. citizens and Green Card holders, tax obligations do not disappear when leaving the United States. In fact, living abroad often means complying with two tax systems simultaneously. Understanding these obligations is essential to avoid penalties and optimize your overall tax position.

Tax Residency: The Starting Point

In both Spain and Portugal, tax residency determines how your income is taxed locally. Generally, you are considered a tax resident in Spain if you spend more than 183 days per year in the country or if your center of economic interests is located there. In Portugal, in addition to the 183-day rule, you may also be considered a tax resident if you have a habitual residence in the country on the last day of the tax year (December 31). Once you qualify as a tax resident in either country, you are taxed on your worldwide income.

At the same time, the United States is one of the few countries that taxes based on citizenship rather than residency. This means that all U.S. citizens and Green Card holders must continue filing U.S. tax returns annually, regardless of where they live.

Core Tax Obligations in Spain and Portugal

For U.S. expats living in Spain, the main obligations include:

• Modelo 100 (IRPF): The Spanish personal income tax return, covering worldwide income.
• Modelo 720: Informative declaration of assets held abroad, required when thresholds are exceeded.
• Wealth Tax (Modelo 714): Applicable depending on region and asset levels.

Spain taxes worldwide income at progressive rates that can exceed 45%, depending on the region and income level.

In Portugal, although the specific forms differ, the structure is similar:

• IRS (Imposto sobre o Rendimento das Pessoas Singulares): The annual income tax return covering worldwide income for residents
• Reporting obligations for foreign assets may apply under international information exchange frameworks
• Wealth taxation is generally more limited compared to Spain, but property-related taxes may apply

Portugal has historically offered attractive regimes for expats, such as the Non-Habitual Resident (NHR) regime, although recent reforms have modified its scope.

U.S. Filing Obligations: Regardless of whether you live in Spain or Portugal, U.S. tax compliance remains mandatory. The key requirements include:

Form 1040 – U.S. Individual Tax Return

All U.S. taxpayers must file Form 1040 annually, reporting their worldwide income, even if they already pay taxes abroad.

The standard deadline is April 15, but you have an automatic extension for expats until June 15 and also you might consider an additional extension available until October 15

FBAR (FinCEN Form 114)

If the total value of your non-U.S. financial accounts exceeds $10,000 at any point during the year, you must file the FBAR. Failure to comply can result in significant penalties.

Additional Forms (if applicable)

Depending on your financial situation, additional reporting may be required:

• Form 8938: Foreign financial assets reporting (similar to the FBAR)
• Form 5471: Ownership of more than 10% in foreign company
• Form 8621: Investments in foreign mutual funds (PFICs)

Avoiding Double Taxation

Although expats must file in both jurisdictions, they are generally protected from double taxation through:

• Tax treaties (Spain–U.S. and Portugal–U.S.)
• Foreign Tax Credit (FTC): Allows you to offset U.S. taxes with taxes paid abroad.
• Foreign Earned Income Exclusion (FEIE): Allows exclusion of a portion of earned income from U.S. tax.

In practice, countries like Spain—with higher tax rates—often generate excess foreign tax credits, reducing or eliminating U.S. tax liability, in Portugal it might depend on you tax regime.

Special Regimes for Expats

Spain offers a special regime for inbound workers (commonly known as the Beckham Law), allowing qualifying individuals to be taxed as non‑residents at a flat rate (generally 24%) on Spanish-source income.

Portugal’s NHR regime has been widely used by expats for its favorable tax treatment on foreign income. Although changes have been introduced, transitional or replacement regimes may still provide tax advantages depending on timing and eligibility.

Reporting Foreign Assets

Spain, Portugal, and the United States impose strict reporting requirements on residents with assets held abroad:

• Spain – Modelo 720: Requires disclosure of foreign bank accounts, investments, and real estate when the value of each category exceeds €50,000.
• Portugal – Foreign Asset Reporting: While Portugal does not have an exact equivalent to Spain’s Modelo 720, tax residents are required to report worldwide income and may need to disclose foreign bank accounts, securities accounts, and other assets within their annual income tax return (IRS). In addition, financial institutions report account information under international automatic exchange agreements (CRS), increasing transparency and compliance oversight.
• United States – FBAR & Form 8938: U.S. taxpayers must file the FBAR if foreign accounts exceed $10,000 at any point during the year, and may also need to file Form 8938 to report specified foreign financial assets

These obligations are primarily informational but carry significant penalties in case of non-compliance, making accurate and timely reporting essential.

Staying Compliant: Common Pitfalls

Many expats face challenges due to:

• Assuming taxes are only due in their country of residence
• Failing to report foreign accounts or investments
• Investing in non-U.S. funds without understanding PFIC rules
• Missing filing deadlines or extensions

Additionally, timing differences between tax systems (calendar vs. fiscal years, reporting thresholds, etc.) can complicate compliance.

The Role of Tax Treaties

Tax treaties play a crucial role in preventing double taxation and clarifying how income is taxed between the United States and your country of residence. Both Spain and Portugal have signed tax treaties with the U.S., which determine which country has the primary right to tax specific types of income.

Under these treaties, the general principle is that tax residency takes priority. This means that if you are considered a tax resident in Spain or Portugal, most types of income will be taxed in that country first. However, because the U.S. taxes based on citizenship, you are still required to report that same income on your U.S. return.

The treaties then allow mechanisms to avoid double taxation, mainly through:

• Foreign Tax Credits: You can offset U.S. tax with income tax paid in Spain or Portugal, often eliminating U.S. liability when foreign taxes are higher
• Allocation rules: Certain types of income—such as employment income, pensions, dividends, and capital gains—are assigned to one country or shared under specific rules
• Tie-breaker rules: These determine residency when both countries could claim you as a tax resident

For example, employment income is typically taxed in the country where the work is performed, while pensions and investment income may follow different rules depending on the treaty provisions. In the case of Spain, the tax treaty explicitly outlines how income should be allocated between the two countries based on residency and source.

It is important to note that U.S. citizens are subject to a “saving clause” in these treaties. This clause allows the United States to continue taxing its citizens as if the treaty did not exist, with some exceptions. As a result, tax treaties do not eliminate the obligation to file in the U.S., but they do provide tools to avoid being taxed twice on the same income.

In practice, proper use of treaty provisions—combined with credits and exclusions—can significantly reduce overall tax liability. However, misinterpretation of treaty rules is a common issue among expats, making professional guidance essential.

US Tax consultants White Paper

For a more detailed and practical breakdown of these obligations, including step‑by‑step guidance, filing thresholds, and key forms, we recommend reviewing our comprehensive whitepaper on U.S. expat taxation in Spain. It provides an in‑depth analysis of both Spanish and U.S. compliance requirements, common pitfalls, and planning opportunities for expats. You can access the full guide here: //ustaxconsultants.es/whitepaper/

Final Thoughts

Living in Spain or Portugal as a U.S. expat provides tremendous personal and financial opportunities—but also requires careful tax planning. The interaction between two tax systems, multiple reporting obligations, and complex international rules makes professional guidance highly advisable.

Ensuring compliance not only avoids penalties but also allows you to take advantage of available tax relief mechanisms, ultimately optimizing your global tax position.

For more information, you can contact us US Tax Consultants. Do not hesitate to contact us by phone at +34 915 194 392, by email at info@ustaxconsultans.es , or through a free consultation, which can be booked via the “Book a free appointment” link on our website.