Double Taxation Treaties: How to Avoid Paying Tax Twice on the Same Income in Spain

Living, investing, or running a business in Spain as a foreigner brings up a question that sooner or later comes knocking: if I already declare this income in my home country, do I have to pay tax on it again in Spain? The short answer is that, barring an error or a gap in knowledge, you shouldn’t have to. Spain has signed double taxation treaties with more than ninety countries, and it’s precisely these treaties that divide up the right to tax a given piece of income between the two states involved. Understanding them — and knowing how to invoke them correctly — is one of the most cost-effective pieces of tax planning an expat, digital nomad, or non-resident investor can do.

What a double taxation treaty is and how it works

A double taxation treaty (DTT) is a bilateral agreement between Spain and another country that sets out, income type by income type, which state has the primary right to tax: the country where you’re tax resident, or the country where the income is generated (the “source” country). Most of the treaties Spain has signed follow, with some variations, the OECD model, so they share a recognizable structure: different rules for salaries, pensions, dividends, interest, royalties, rental income, or capital gains from property sales. A treaty doesn’t replace Spanish law, but it does take precedence over it when the two conflict: if the treaty says a given income is only taxable in your home country, the Agencia Estatal de Administración Tributaria (AEAT, Spain’s national tax agency) cannot also claim it in Spain, and vice versa. The usual problem isn’t that the treaty doesn’t exist — it’s that the taxpayer, or the Spanish payer, doesn’t realize it needs to be invoked.

The tax residency certificate: the key that unlocks the treaty

To benefit from a treaty, you need to prove, with an official document, where you’re tax resident. That document is the tax residency certificate, issued by your home country’s tax authority (not by Spain), which confirms that you’re taxed there on your worldwide income for a given period. Without that certificate, the Spanish side — whether it’s a bank, an employer, or the AEAT itself — will apply the default withholding or general tax rate, without the treaty’s benefits, and recovering that excess afterward means going through a refund procedure that can take months. The recommended approach is to request the certificate every year from your home tax authority and present it, depending on the situation, either to whoever pays you in Spain (so a reduced withholding rate is applied from the outset) or directly alongside your tax return — whether that’s the personal income tax return (IRPF) if you’re a resident in Spain, or the Non-Resident Income Tax (IRNR, typically filed via Form 210) if you’re not.

Exemption versus tax credit: the two methods for not paying twice

When a treaty doesn’t reserve a given income exclusively to one country, one of two mechanisms kicks in to eliminate double taxation. Under the exemption method, the country of residence simply doesn’t tax (or exempts) income that’s already been taxed in the other country, although it sometimes still factors it in when calculating the rate applied to your other income. The tax credit method — also called the “foreign tax credit” or “deduction for international double taxation” — works differently: the country of residence does include that income in your taxable base, but lets you subtract the tax already paid abroad from your tax bill, capped at what you would have paid in Spain on that same income. For its residents, Spain mostly applies the tax credit method under the IRPF: you declare your worldwide income and then apply the deduction for taxes already paid abroad, always with the treaty and supporting documentation in hand. Which method applies in a given case isn’t up to the taxpayer to choose — it’s determined by the treaty itself, income type by income type, so it’s worth reviewing the details carefully before assuming anything.

At Zythos Business, we help self-employed professionals and small businesses with partners, clients, or income outside Spain identify which treaty applies, obtain the corresponding tax residency certificate, and apply the correct method — exemption or credit — both to withholdings and to the annual return, so that no income ends up taxed twice.