What it means that Bizkaia has rules of its own
The Concierto Económico, the economic agreement between the Basque territories and the Spanish State, recognises the historical territories' capacity to regulate and collect their own taxes. Bizkaia has its own Norma Foral on personal income tax, with its scale, its reliefs and its deductions, which do not match those of the territorio común — the common-regime territory that covers most of Spain. It also has its own corporation tax and its own regulation of inheritance and gifts.
The everyday consequence is that the form a self-employed person files in Bilbao is not called the same and is not filed in the same place as the one a self-employed person files in Burgos, and that the dates of the annual income tax campaign need not coincide either. What you find searching in Spanish on the internet nearly always describes the common regime: for Bizkaia it is no use.
Not everything is provincial, and that is where the tangle is
The Concierto shares things out: there are taxes demanded in full by the provincial council, others where the applicable rules remain the common ones even though the administration is provincial, and situations where the split depends on the volume of operations or on the tax address. A company operating on both sides can end up filing with both administrations in proportion.
That is why the first thing we look at in a Bizkaia case is not the tax: it is where your tax address is and where your operations are deemed to be carried out. When that is wrong, everything downstream comes out wrong.
A word on terminology, because these names get translated badly. Territorio común is the ordinary Spanish tax system, administered by the state tax authority and covering most of the country. Territorio foral means Álava, Bizkaia, Gipuzkoa and Navarre, each with its own legislature for tax and its own administration. The two systems coexist and share taxpayers, and the boundary between them is drawn by the Concierto and the Convenio, not by where you happen to file.
Our work is common-regime Spanish tax and international tax. If your case is entirely provincial — your Bizkaia income tax, your provincial corporation tax, your Biscayan estate — the honest thing is to say so: you are better served by a firm here, and we say it in the first email instead of learning at your expense. We coordinate with the provincial firm you appoint. Where we add something is in what crosses borders and in what remains a state matter.
Where we do fit: the international and the state layer
A double tax treaty is read the same way in Bilbao as in Seville, and the underlying questions of someone with accounts, securities or property outside Spain, or shares in a foreign parent, are the same. What changes is where they are answered: a Bizkaia resident files with the provincial tax office, on its own forms and to its own calendar, including the reporting of assets held abroad; and the Concierto Económico splits even the tax of a non-resident owning a flat here between the Diputación and the State. That is why we work on those fronts alongside the provincial adviser, who is the one who files.
Those are the three fronts we usually come into, normally alongside the client's own provincial adviser. They are in Modelo 720, stock options and RSUs and non-residents.
Who writes to us from Bilbao
| Who | What they usually face |
|---|---|
| Engineer back from a posting abroad | Tax residence in the year of return, the treaty and the declaration of assets held abroad |
| Executive with shares in a foreign parent | How and when the equity is taxed, and which part is provincial and which is not |
| Company invoicing on both sides of the Ebro | The split by volume of operations between provincial and state administration |
| Non-resident owner with a flat in Bilbao | Modelo 210 per property and per owner, with imputed income for the days not let |
| Heir to a relative with assets outside Spain | Which rules apply, valuation and coordination with the notary |
How we work with clients in Bilbao
Coordinated, not overlapping. If you already have a provincial adviser we talk to them and keep the international or state part of the file; if you do not have one and your case needs it, we tell you to find one. That is less business for us and fewer problems for you.
What we are never going to do is improvise a provincial rule we do not handle or quote you an article from memory. In this field an approximate figure is a wrong figure.
On our side the routine is the usual one: paperwork in writing, figures before filing and one person answering. On the provincial side we ask you to appoint a local firm and we talk to them directly, so that nothing sits in the gap between the two. We guarantee no outcome before either administration, and we say which parts of a position we regard as arguable.
Moving from Madrid to Bilbao mid-year: which tax authority is yours in 2026
The question we hear most from Bilbao in summer is not about a particular tax but about a date. An engineer leaves Madrid and starts work in Bizkaia. The main rule of the Concierto Económico — the agreement under which the Basque provinces run their own tax systems — for an individual is permanence: you are resident in the Basque Country in the year you spend more days of the tax period there than in the rest of Spain. If days are not enough, the centre of interests and the last declared residence come in.
| Date of the move | Days in Madrid | Days in Bizkaia | 2026 income tax |
|---|---|---|---|
| 1 May | 120 | 245 | Foral, with the Bizkaia tax authority |
| 1 July | 181 | 184 | Foral, by three days |
| 1 August | 212 | 153 | Common, with the state tax authority; foral from 2027 |
The second row is the one to watch: three days decide which rules apply to the whole year. If you can choose the date of the move, it is worth knowing beforehand; and if the change of address is made only to pay less and does not reflect reality, it has no effect. In the year of the move, if the common system still applies to you, we prepare the 2026 return; from then on, the foral return is handled by your Bizkaia adviser, with whom we coordinate.
How we share a Bilbao case with your foral adviser
| Matter | Who handles it |
|---|---|
| Income tax for the year you were still resident in common territory | Us |
| Bizkaia foral income tax from the time you live here | Your foral adviser |
| A flat in Madrid, Málaga or Valencia: plusvalía municipal, inheritances where the deceased lived in common territory | Us |
| Reading the double tax treaty and the other country's certificates | Us, and we pass on the result |
| Any figure, deduction or deadline under the foral rules | Your foral adviser |
If your case has a leg in common territory or outside Spain, tell us about it through the form for international freelancers or the one for inheritances and gifts, whichever fits.
This split is put in writing at the start, with the name and email of each party, so that no deadline is left in no man's land. And if a matter does not clearly belong in one of the two columns, we say so there and then rather than assuming out of habit: the border between foral and common is where deadlines get lost.
Someone returning from a posting abroad with accounts, a company pension plan or shares with a foreign broker usually searches the internet for the state tax authority's Modelo 720. But the reporting duty is imposed by the administration competent for your residence, and if you live in Bizkaia that administration is the foral one, with its own rules and its own form. Filing with the wrong administration does not meet the obligation. What we do contribute is the inventory: what you hold, where, with what balances at 31 December and with what documents; with that, your foral adviser files at the foral office. If you return in a year in which you were still resident in common territory, then it is our Modelo 720.