How the US-Spain Tax Treaty Actually Taxes Your Interest Income

Passive Income and the Expat Tax Puzzle

Many international tax conversations with expats start with earned income - wages, self-employment, business profits, ect. It usually moves directly into how to make sure that income doesn't get taxed twice through the Foreign Earned Income Exclusion or the Foreign Tax Credit. But that's one half of the picture. The other half, the one that trips up a lot of clients, is passive income: the interest, dividends, and capital gains sitting in a US brokerage account you kept after you moved abroad.

Say you move to Spain and become a Spanish tax resident, but you still have a US brokerage or bank account. That account is still generating interest and dividends. Spain is going to tax that income, because it's the country where you now live. But the US is going to tax it too, because you're still a US citizen. Neither country is wrong to claim it - that's exactly the scenario a tax treaty exists to sort out.

Here's the part people get wrong going in: the treaty usually isn't a tool for getting a US citizen out of tax entirely. What it does is assign which country has primary taxing rights and tell you who owes a credit to whom. I had a client run into this exact situation with Spain recently, so I'll walk through it the way I actually worked it - using the real treaty language - because the process holds regardless of which country you're dealing with.

The treaty usually isn't a tool for getting a US citizen out of tax entirely. What it does is assign which country has primary taxing rights and tell you who owes a credit to whom.

The Saving Clause: The Rule That Changes Everything

Before you get anywhere near the article covering your specific type of income, there's a provision buried in Article 1 of every US tax treaty that affects the entire analysis: the saving clause. Article 1, Paragraph 3 of the US-Spain treaty says the US can tax its own residents and citizens as if the treaty had never been signed. Specifically it says:

Notwithstanding any provision of the Convention except paragraph 4, a Contracting State may tax its residents (as determined under Article 4 (Residence)), and by reason of citizenship may tax its citizens, as if the Convention had not come into effect.

Read that again, because it's easy to miss what this really means - you can spend an hour working through a treaty article and easily miss the fact that the saving clause hands the US full taxing rights back in the very beginning.

There are exceptions to the saving clause, and certain types of income carve themselves out in paragraph 4, but interest isn't one of them. So before I look at anything else, I check whether the saving clause applies, and I confirm residency status under Article 4. If the person weren't actually a Spanish tax resident under the treaty's definition, Spain wouldn't have a claim on this income at all, and the whole exercise collapses back to US-only taxation. Assuming residency is established, the saving clause is live, and it's going to matter later.

What this means in practice, before you even get to the income-specific article:

• The US can tax its own citizens and residents as if the treaty were never signed
• Only specific, limited types of income are carved out as exceptions
• Interest income is not one of those exceptions
• Residency under Article 4 still has to be confirmed, or the analysis doesn't get this far

Why Residency Under Article 4 Matters Here

That last point is worth unpacking, because it's easy to assume residency is settled the moment someone moves abroad - it isn't. At least not for treaty purposes. Article 4 defines who actually counts as a "resident of Spain" under the treaty, and that's a specific legal test, not just a description of where someone happens to be living. Generally, it means being liable to tax there by virtue of domicile, residence, or a similar connection under Spain's own domestic law - holding a visa or renting an apartment doesn't automatically get someone there.

This matters because Article 11 only gives Spain the right to tax this interest income if the recipient qualifies as a Spanish resident under that definition. If they don't, Spain has no claim on the income at all: i.e. no double taxation to relieve, no credit to calculate, no resourcing to work through. It's simply US tax. It also comes up when someone keeps real ties to the US - a home, a spouse, financial accounts - while also meeting Spain's residency test; most treaties, this one included, resolve that with a tie-breaker test looking at things like permanent home, closer personal and economic ties, and time spent in each country. We’ve written tons of articles on international residency - it’s always worth confirming when the concept comes up.

Article 11: How Interest Income Gets Taxed

Now go to the article that actually covers the income type - for interest, that's Article 11. It says interest arising in the US and paid to a resident of Spain may be taxed in Spain. So far, so simple: Spain gets to tax it. But the next sentence adds a wrinkle - the interest may also be taxed in the US, the country where it arose, and if the beneficial owner is a Spanish resident, that US tax is capped at 10% of the gross amount. In practice, that 10% usually shows up as withholding.

Read on its own, that's a good result: Spain taxes the income, and the US is limited to 10%. But this is where the saving clause comes back into play. Because our client is a US citizen, not just a Spanish resident, the US isn't actually limited to that 10% - the saving clause overrides it, and the US retains the right to tax the full amount, same as if the treaty didn't exist.

So at this point, both provisions have effectively canceled each other out:

• Spain, as the country of residence, may tax the interest
• The US, as the country where the interest arose, may also tax it - capped at 10% of the gross amount for a non-citizen
• The saving clause removes that cap for a US citizen, restoring the US's right to tax the full amount

We're right back where we started: both countries can tax the full amount, and nothing in the treaty so far has actually prevented double taxation.

Article 24: The Relief-From-Double-Taxation Mechanism

This is where Article 24, the relief from double taxation, comes to save the day.

“In the case of an individual who is a citizen of the US and a resident of Spain, income which may be taxed in the US by reason of citizenship in accordance with paragraph three,"

That's the saving clause (Article 1) -

"shall be deemed to arise from Spain to the extent necessary to avoid double taxation."

The key language says that income the US taxes by reason of citizenship - exactly the scenario the saving clause creates - is deemed to arise in Spain instead, to the extent necessary to avoid double taxation. That's the resourcing concept: income that would normally be sourced to the US gets treated as Spanish-source for credit purposes, which lets the US tax paid actually offset against a US credit correctly.

But the next section adds in some limitations.

“Provided that in no event will the tax paid to the US be less than the tax that would be paid if the individual were not a citizen."

We just read about this in Article 11, so here’s what it means.

• Income the US taxes by reason of citizenship is deemed to arise in Spain instead, for credit purposes
• The US tax still can't drop below what a non-citizen would have paid - the 10% from Article 11
• So the US keeps that 10% no matter what, and Spain has to credit it

That floor is the detail people miss most often - it's tempting to assume resourcing wipes out the US tax entirely, and it doesn't.

Interest tends to have a fairly clean, blanket resourcing rule like this one. Dividends are messier - a lot of treaties split dividend income with the US keeping a flat percentage and the other country taxing the remainder, rather than a straightforward resourcing-and-credit mechanism. The underlying logic is the same, but the math looks different depending on the income type.

A Worked Example: $100 of Interest, Two Countries

To put some real numbers on it:

• Interest income: $100
• Spain's tax (30%): -$30
• US tax under the treaty-capped rate: -$10
• Spain's credit for the US tax paid: +$10
• Spain's net tax after the credit: -$20
• Total tax paid, both countries combined = -$30

That total - $20 to Spain, $10 to the US, $30 combined - is exactly what Spain's domestic rate would have produced on its own.

The treaty didn't reduce the tax bill. It splits it correctly between the two countries and makes sure neither one taxes the full amount independently of the other.

Working With Advisors in Both Countries

None of this happens automatically. Both a US return and a Spanish return have to be drafted with the other one in mind - the US return needs to reflect the Spanish tax paid, and the Spanish return needs to reflect the US tax paid, so the credits line up on both sides and the total tax doesn't exceed what the treaty allows. This kind of planning is a coordination exercise between two countries, which means it only works well when the advisors on both ends are actually talking to each other, or at least understand how the other side's system works.

I ran into the practical version of this recently. I laid out this exact analysis for a Spanish accountant working for a client, and they just weren’t comfortable taking this credit. The position was defensible, but the accountant didn't want to deal with a Spanish audit over it, and recommended the client just pay the full 30% in Spain instead of taking the treaty position.

That creates a real tradeoff between two paths:

• Pay the full 30% in Spain and claim a full US credit. Safe locally, but it isn't quite what the treaty specifies, and it can raise questions on the US side down the road.
• Take the treaty position as written. Technically correct, but it carries some audit risk on the Spanish side.

In my experience, the right call often comes down to dollar amount. On a small number, I'm not going to push a foreign tax authority into a fight - take the US credit, and if it gets questioned later, it's not much to true up. On a larger number, it's worth finding a second opinion in the foreign country before deciding.

What this usually comes down to is experience, not disagreement about the law.

An accountant who doesn't regularly handle cross-border cases is going to default to the conservative position - pay everything locally - because that's the option that guarantees no problems in their own jurisdiction, even if it's not the technically correct split. That's not a knock on them; it's just not their focus. It's why having people on both sides of the border who actually do this kind of work matters more than most clients realize.

How This Applies Beyond Spain

The specific rates in this example are Spain's, but the method isn't. Any time you're dealing with passive income under a US treaty, the process is the same three steps:

1. Check whether the saving clause applies and confirm residency
2. Read the income-specific article to see how the tax gets split
3. Check the relief-from-double-taxation article for how the credit and resourcing actually work

The article numbers, specific clauses, and percentages shift from treaty to treaty, but the process for working through a treaty holds true across the various countries.

If you're sitting on US-source interest, dividends, or capital gains while living abroad, it's worth having someone walk through this with your specific treaty rather than assuming either country automatically gets it right on its own. Reach out and I'm happy to go through the exact scenario with you.