Before you start

NIE
Padrón registration in Bizkaia, which is what establishes foral residence
Records of worldwide income and foreign assets
Credentials for the Bizkaia foral electronic office, which are separate from state Cl@ve

Step-by-step

1
Understand which authority you belong to
Foral residence follows where you habitually live, established through the padrón. Living in Bilbao makes you a Bizkaia taxpayer. Living forty minutes away in Cantabria or La Rioja puts you back under the Spanish state system with different rates and a different filing platform. The boundary is real and administrative, not notional.
OnlineWho: You
2
Get credentials for the Bizkaia electronic office
The foral treasury runs its own online system with its own identification. State Cl@ve credentials do not get you into it. Set this up early — it is where your return, your notifications and your payment references all live.
OnlineWho: You
3
Find an asesor who works with the Hacienda Foral
Ask the question directly and treat a vague answer as a no. The forms, rates, deductions, deadlines and platform all differ from the state system, and a first filing made on the wrong basis is difficult to unwind. This is the single most consequential piece of local advice for anyone moving here.
In personWho: You
4
Establish your tax residence position for the year
The 183-day test and the centre-of-economic-interests test work broadly as in the rest of Spain, and Spanish tax residence is worldwide. What differs is which authority then assesses you. If you arrive mid-year with substantial foreign income, take advice on the timing before rather than after.
In personWho: You
5
Check the foral wealth tax position
Bizkaia levies its own wealth tax with its own thresholds and reliefs, quite separate from the state design that Madrid and Andalusia rebate. Do not assume that what you have read about Spanish wealth tax rebates applies here in either direction — the foral treatment is its own question.
In personWho: You
6
File the foral annual return in its own window
Bizkaia runs its own filing campaign with its own dates, its own pre-filled proposal and its own appointment system. The deadlines do not necessarily match the state's April-to-June Renta window. Check the foral calendar rather than the national one.
OnlineWho: You

Documents you’ll need

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Bizkaia foral electronic office credentials
Padrón certificate establishing foral residence
Employment income certificates from Basque employers
Records of all worldwide income, foreign accounts, property and securities

Things most newcomers don’t know

You do not file with the Agencia Tributaria, and almost no general guidance says so.

The Concierto Económico gives the Basque provinces the power to set and collect income, corporate, wealth and inheritance taxes themselves. Every article about Spanish tax residency, the Beckham Law, the Modelo 720 or the Renta window is describing the state system. In Bilbao you are dealing with the Diputación Foral de Bizkaia — different rates, different deductions, different forms, different platform, different calendar. This is the defining administrative fact of living here and it is systematically absent from relocation content.

Source: Diputación Foral de Bizkaia

The foral boundary is geographic and it is sharp.

Foral residence follows habitual residence, so living in Bilbao puts you under Bizkaia and living a short drive away in Cantabria puts you under the state system. There is no gradient. For anyone weighing towns on either side of the boundary, or considering a move within northern Spain, the tax consequence of crossing that line is immediate and complete rather than incremental.

Source: Diputación Foral de Bizkaia

The impatriate and nomad regimes you have read about are state regimes.

The Beckham Law and the digital nomad tax treatment were created in state legislation and are administered by the Agencia Tributaria. How, and whether, an equivalent applies to a Bizkaia taxpayer is a separate question with its own answer, and it is not safe to assume the state position carries over. If your move is being planned around one of these regimes, establish the foral position before you commit to living on this side of the boundary.

Source: community-reported

Social security is state, tax is foral — and the split confuses everyone.

Your contributions, your pension record and your healthcare entitlement run through the Spanish Seguridad Social. Your income tax runs through Bizkaia. Two administrations, two portals, two sets of credentials, two calendars. Almost every first-year administrative confusion here comes from assuming a problem belongs to one when it belongs to the other.

Source: Seguridad Social / Diputación Foral de Bizkaia

Common mistakes to avoid

Filing with, or planning around, the Agencia Tributaria when you are a Bizkaia taxpayer.
Hiring a tax adviser who does not work with the Hacienda Foral.
Assuming the state Renta window and deadlines apply to your foral return.
Assuming state-level impatriate or nomad tax regimes carry over unchanged.
Assuming what you have read about Spanish wealth tax rebates describes the Bizkaia position.

Some of this may be out of date. Spotted something inaccurate? Help us keep it right for the next newcomer.