Double Taxation Treaties: How to Avoid Paying Taxes Twice in Spain

If you live in Spain but collect rental income back home, work remotely for a foreign company from Málaga or Valencia, or hold investments split across two countries, you’ve probably asked yourself this question: do I have to pay tax on that same income in both places? The short answer is that, barring a filing mistake, you shouldn’t. That’s exactly what double taxation treaties (DTTs) are for — bilateral agreements Spain has signed with most of its major economic partners, allocating the right to tax each type of income between your country of residence and the country where the income arises. Understanding how they work, and how to invoke them with the Agencia Tributaria (AEAT, Spain’s tax authority), is essential for any foreigner with financial interests in Spain.

How double taxation treaties work

A DTT is an agreement between two states that spells out, income type by income type, which country gets first claim to tax it: the one where you’re tax resident, or the one where the income originates (a salary, a rental, a dividend, a pension). Most of the treaties Spain applies follow the OECD model, so they share a broadly similar structure even though the specific rates vary from treaty to treaty. As a rule, employment income is taxed where the work is physically performed, real estate where the property is located, and dividends, interest or royalties are split between both countries subject to a capped withholding rate at source. The treaty doesn’t remove your obligation to file in both countries if you’re resident in one and earn income in the other — but it does stop you from paying the full amount twice, which is handled by your country of residence through one of the relief mechanisms described below.

One important nuance: tax residency is not the same as legal residency or your residence permit. You can hold an NIE (Foreigner Identification Number, the ID any foreigner needs to operate for tax purposes in Spain) and live here without being a tax resident, or the other way around. As a general rule, Spain applies the 183-days-a-year test, alongside where your main economic interests or family are based. Working out which country you’re tax resident in is the first step — and sometimes the most contentious one — before any treaty provision can even apply.

The tax residency certificate: your key to the treaty

To get a foreign payer (a bank, a tenant, a company) to apply the reduced withholding rate set out in the treaty, or to prove to the AEAT that you’ve already paid tax abroad, you need a specific document: the tax residency certificate. It’s issued by the tax authority of your country of residence — in Spain, by the AEAT itself — and confirms, for a given year, that you’re tax resident there for treaty purposes. Without it, the source country will typically withhold at the higher general rate, leaving you to claim a refund afterward — a slower process than requesting the reduced rate upfront. It’s worth requesting a new certificate every year and keeping it on file alongside the paperwork for each piece of foreign income, since many payers require it as a precondition.

Exemption vs. credit: the two routes to avoiding double taxation

When you report income in your country of residence that’s already been taxed elsewhere, the treaty sets out one of two ways to correct the double taxation. The first is the exemption method: the foreign income isn’t taxed again in your country of residence, though it’s usually still factored in when calculating the rate applied to your other income (known as exemption with progression). The second is the credit method: you declare the full foreign income in your country of residence, but deduct the tax already paid abroad from your final bill, capped at what you would have paid had that income been earned entirely in Spain. In Spain, this is implemented through the deduction for international double taxation, within personal income tax (IRPF) or corporate tax. Which method applies isn’t your choice — it’s fixed by the specific treaty depending on the type of income — which is why it’s worth checking the treaty with the country of origin before taking any figure at face value.

Between establishing the right tax residency, getting the certificate sorted in time, and applying the correct relief method, there are several places where a slip can end up costing money — either through overpayment or exposure to an AEAT review. At Zythos Business, we support self-employed professionals and small businesses with cross-border activity through exactly this terrain: we review which treaty applies, what documentation to request, and how to reflect it correctly on each tax return, so that operating across countries stops being a source of tax surprises.