Sophie Lambert is a Belgian illustrator who, since 2024, has spent a good part of the year in a rented studio in Cádiz. She has filed income tax returns in Spain since then, and in 2026 the Agencia Tributaria, the Spanish tax agency, issued her a certificate of tax residence without any trouble. In Brussels she keeps her flat, her partner and the company through which she invoices some commissions, and her own administration has also issued her a residence certificate for the same year. A gallery in Amsterdam that is going to pay her 30,000 € for a series of works asks her for "the residence certificate", in the singular. Sophie has two and does not know which to send.
Sophie's question has an uncomfortable answer: neither of them prevails. A certificate proves what one administration sees in its data; it does not decide a conflict between two States.
What a certificate is worth in law
Article 75 of the Regulations on tax management and inspection (Royal Decree 1065/2007) gives tax certificates an informative character: they produce the effects stated in them and those established by the rule that governs them. The Spanish Agencia certifies residence when its data support it under Spanish law. The Belgian administration does the same under its own law, on which we express no view: that is for Sophie's adviser in Belgium to confirm.
Neither document binds the other State. Holding both only proves that the two administrations, each under its own law, see Sophie as resident. In other words, it documents the conflict instead of resolving it.
| Instrument | What it does | What it does not do |
|---|---|---|
| Spanish certificate | Proves that, on the Agencia's data, Sophie lives in Spain | Bind Belgium |
| Belgian certificate | Proves the same according to the Belgian administration | Bind Spain |
| Treaty tie-breaker rules | Say to which State residence is allocated for treaty purposes | Apply by themselves: someone has to invoke and prove them |
| Mutual agreement procedure | Lets the authorities of both States agree on the solution | Guarantee an agreement within a fixed time |
The cost of leaving it alone
Suppose both States tax the gallery's payment as a resident's income.
- Amount received: 30,000 €.
- Share of Sophie's Spanish tax attributable to that income, according to her return: 7,200 €.
- Tax that, as her Belgian adviser calculates it, would be charged there on the same income: 8,100 €.
- Total paid on the same income if nobody gives way: 7,200 + 8,100 = 15,300 €.
- What she would pay if only one State taxed it as a resident: between 7,200 € and 8,100 €, depending on which.
The difference, some 7,000 or 8,000 € on a single transaction, is the price of not resolving dual residence. And it is repeated with every item of income in the year.
The double taxation relief in article 80 of the IRPF Act (the Spanish personal income tax) is not designed for this scenario. It allows a deduction for tax paid abroad on income obtained there, but it does not resolve two States each claiming the same person as resident on their entire worldwide income. That is what treaties are for.
How the treaty resolves it
The residence article of the treaty between Spain and the other State contains tie-breaker rules that allocate residence to only one of them for treaty purposes: permanent home, centre of vital interests, habitual abode, nationality and, as a last resort, agreement between the authorities. How to prepare the evidence for each criterion is explained in two countries consider me resident: who gives me the certificate?, and the guide on dual residence conflicts develops it.
What matters here is that those rules are not applied by an official when issuing a certificate. They are invoked by the taxpayer, normally when one of the two States assesses them or sends a formal request.
The mutual agreement procedure
The first additional provision of the Non-Resident Income Tax Act (IRNR) states that disputes with the administrations of other States over the application of treaties are resolved through the mutual agreement procedures provided for in the treaties themselves, without prejudice to any appeals that may lie. For disputes with other European Union States, the same provision also refers to the mechanisms of Directive (EU) 2017/1852.
The detail is in Royal Decree 1794/2008. Two practical points:
- Who handles it in Spain. As a general rule, the Dirección General de Tributos (the Directorate General for Taxation, part of the Ministry of Finance) is the competent authority, under its article 2.
- When to request it. Article 8 refers to the time limit set by each treaty, counted from the day after notification of the assessment, or equivalent act, that results or may result in taxation not in accordance with the treaty. The time limit differs from treaty to treaty, so it should be read as soon as the first assessment arrives.
The procedure guarantees neither an outcome nor a date. The authorities may take a long time and, in procedures based solely on the treaty, they are not always obliged to reach agreement.
If you already have two certificates, or an assessment from one of the States, and would like us to review your position before the time limits run, you can tell us about it in the certificate form. We coordinate with the adviser you appoint in the other country.
The temptation is to send the Spanish certificate to one payer and the Belgian one to another, depending on which withholding comes out lower. That leaves a trail of contradictory statements that either administration can use later. While residence remains unresolved, the prudent course is not to invoke the treaty before third parties with either document without first analysing the tie-breaker criteria.
So what does Sophie send the gallery?
First, find out exactly what the gallery is asking for and why: if it is to apply a treaty with the Netherlands, she needs a treaty certificate from her State of residence. Second, decide, with the tie-breaker analysis done, which State is her State of residence for treaty purposes. Third, ask that State for the treaty certificate. If there is no reasonable conclusion, the honest course is to tell the gallery so and accept the withholding that applies without a treaty while the matter is resolved.
We explain the difference between the two kinds of certificate in ordinary and treaty certificates.
What paperwork to organise in the meantime
A mutual agreement procedure is won or lost on paper. While the conflict remains open, it is worth gathering the calendar of days in each country, the agreements for both homes, evidence of where the work is carried on, the returns filed in both States and every assessment and formal request received, with its date of notification. That last date is what starts the treaty time limit running, and losing it for want of a note is one of the most expensive mistakes there is.
A case apart: tax havens
For Spanish nationals who move their residence to a country or territory classed as a tax haven, article 8.2 of the IRPF Act provides that they do not lose their status as taxpayers in the year of the move or in the following four years. In that case, holding a certificate from the new territory does not change taxation in Spain during that period. And article 9 allows the administration to require proof of 183 days' presence in the territory in question.
The Salama Tax page describes the certificate and its uses. In a case of dual residence nobody can promise which State will win; what can be done is to avoid making your position worse while it is resolved.