Short answer: the ISV age reduction only applies to cars registered in a European Union member state. A car coming from Switzerland, the UK, the USA or Japan pays the full ISV — even if it is 10 years old. It is the most expensive mistake in importing, and almost every online simulator (ours included, until a few days ago) made it silently.
Why age doesn't count outside the EU
The well-known 20%–80% reduction on the ISV by years of use exists for a reason of EU law: Portugal cannot penalise a used car that has already been driven in another EU country. That protection does not cover third countries. A Swiss car is not a "European used car" in the eyes of the tax — it is taxed as if age didn't exist.
A real (and costly) example
A Mercedes E 350, petrol, 4663 cc, 213 g/km CO2, first registered 2016. As an EU car, with the 10-year 80% reduction, the ISV would be about €6,076. As a Swiss car, with no reduction, the real ISV is €30,378 — five times more. We confirmed both figures to the cent on the official AT simulator. And that is before customs duty (~10%) and VAT (23%) on price + duty + ISV, which only apply to non-EU imports.
The exception that changes everything: transfer of residence
If you are moving your residence to Portugal, the ISV can be €0 (transfer-of-residence exemption, Art. 58–61 of the CISV) — and this applies to non-EU countries too. All conditions are required: prior residence abroad ≥ 12 months; the vehicle in your name and used ≥ 6 months before the move; acquired under normal taxation at origin; the request within 12 months of settling; and no selling for 12 months. It is not automatic — but for someone who is genuinely relocating, it turns a cost of tens of thousands of euros into close to zero.
We found the bug in our own simulator — and fixed it
Until a few days ago our calculator had no country of registration selector. As a result it always assumed "EU" and applied the reduction to every car, Swiss ones included. It was a client with a Swiss car who made us look twice. We fixed it: there is now a EU / Non-EU selector, and for non-EU cars the simulator shows the full ISV and warns about duty and VAT. We would rather say this out loud than pretend it never happened — transparency is the name on the door.
Don't trust — verify
The formula behind our ISV and IUC calculators is the official one, and it is open: you can read the code, run the tests and compare with the AT. We have:
- the calculator's open source — github.com/claracarspt/calcs;
- a free public API for your own site or tool;
- an MCP server so AI assistants can compute ISV/IUC directly;
- the step-by-step methodology, with the tables and the law's articles.
If you want the right number for your case — including a non-EU import or a change of residence — run it here or talk to us. We do the full maths, even when the number isn't the one we'd like to show.
