Carlos is an IT consultant in Madrid. In February 2025 he bought a new car, a mid-range passenger car, for €30,000 plus €6,300 of VAT. He uses it to visit clients and also to take his children to school and for holidays. His gestoría (the administrative and tax agencies many Spaniards use for their paperwork) deducted the full €6,300 in the 303, the quarterly VAT return, for the first quarter of 2025. In September 2026, when he changed adviser, the new one warned him that the deduction was probably wrong. Carlos wanted to know three things: whether it really was a mistake, how much it would cost to fix and whether he could ask the gestoría to bear it.
First things first: is it really a mistake?
Not everything a second adviser sees as wrong actually is, and it is worth starting here before blaming anyone. The Spanish VAT Act, in its article 95, presumes that passenger cars are used for the business to the extent of 50 %. That presumption can be rebutted, and there are vehicles the law presumes to be 100 % business use: those carrying goods, those carrying passengers or used for driving tuition, those used by sales representatives or agents, among others.
Carlos falls into none of those categories and also uses the car in his private life. To defend more than 50 % he would have to prove greater professional use, with travel records he does not have. So yes: deducting 100 % was a mistake, and the correct figure was half.
What correcting it on his own initiative costs
- VAT deducted: €6,300.
- VAT that could be deducted: 6,300 × 50 % = €3,150.
- Excess to be returned to the tax office: €3,150.
- Time elapsed: the filing period for that quarter ended in April 2025; by September 2026 more than twelve months have passed, so the article 27 recargo (the surcharge for correcting late but unprompted) is 15 %: 3,150 × 0.15 = €472.50.
- With the 25 % reduction for paying on filing: €354.38.
- Late-payment interest: only for the time beyond the twelve months, about five. At an interest rate of 4 % for the sake of the example: 3,150 × 0.04 × 5/12 = €52.50.
- Total cost of the regularisation: 3,150 + 354.38 + 52.50 = €3,556.88.
The 2025 VAT is corrected with a supplementary self-assessment for the quarter affected, not by putting the difference into the current 303. And it is worth reviewing the car's running costs at the same time (fuel, repairs; not insurance, because it carries no VAT), which were probably deducted on the same 100 % basis. If you would like us to go through your quarters with that magnifying glass, the self-employed form is the place.
Whom the tax office claims from, and whom Carlos can claim from
The person liable for the VAT is Carlos. The gestoría filed in his name, with his authorisation or as a registered filing collaborator, but it does not come to owe anything to the tax authorities for having got it wrong. The tax office will collect the excess, the surcharge and the interest from Carlos and, if it discovers the mistake itself in a check, a penalty as well. That is the main reason to correct first: without a prior request there is no penalty, and once there is a request the argument «it was my adviser» is taken into account, but not accepted automatically. The difference between the two situations is explained in surcharge versus penalty.
Against the gestoría, the route is civil. Carlos had a services contract with it, and if the service was provided negligently he can claim the damage it caused him. Not everything he pays is damage.
| What Carlos pays | Amount | Damage attributable to the adviser? |
|---|---|---|
| Excess VAT deducted | €3,150 | No: he was never entitled to deduct it |
| Reduced 15 % surcharge | €354.38 | Yes |
| Late-payment interest | €52.50 | Debatable: it offsets the fact that he had that money |
| New adviser's fees for the correction | As quoted | Yes |
| Penalty, if there were one | Variable | Yes, if the mistake was the adviser's |
What almost nobody tells you is that, with deduction errors like this one, the loss you can claim is small compared with the fright. Carlos has not lost €3,150: he had it for a year and a half without being entitled to it. What he has lost is €354.38 of surcharge, the cost of putting it right and, above all, time. Framing the claim in those terms makes it credible, and it is the best way to negotiate with an insurer.
Building a claim that stands up
What has to exist in writing
- The engagement letter or quote describing the service: if it included filing the 303, the mistake falls within what was contracted.
- The email or message with which Carlos sent the car invoice. If in it he explained that the car was also the family car, so much the better.
- The filing receipts for the 303 concerned, downloaded from the tax agency's online office, with their secure verification code.
- The fee invoices paid to the gestoría during that period.
- The regularisation calculation and the receipts for payment of the surcharge and the interest.
How it is put forward
First, a written claim to the gestoría, with the documents and the specific figure, asking it to pass it to its professional liability insurer if it has one. Many do, and activate it without argument when the mistake is clear and the figure reasonable. If there is no answer or it refuses, the courts remain, a route whose cost only makes sense if the amount justifies it. The general period for claiming for breach of contract is five years.
The day you decide to change adviser, the previous one loses any incentive to help you. Before telling them, download yourself from the Agencia Tributaria's online office every return filed in your name, ask in writing for the VAT registers and the invoices you gave them, and check which authorisations they hold. Then revoke them. Rebuilding a file without the cooperation of whoever kept it is much slower and more expensive.
How long a 303 can be corrected
The tax authorities' right to check and assess a quarter lapses after four years, counted from the day after its filing period ends. Carlos is well within that window, and will be until 2029. That means two things: the mistake can surface in any check between now and then, and correcting it first gives him control over the timing and the cost. The other way round, if the mistake had been in his favour (deductible VAT that was not deducted), the time limit to use it is also four years from when the right arose. The guide on the four-year limitation period explains how it is counted and what interrupts it.
During those four years, moreover, it is advisable to keep the invoices and registers that support each deduction: if the mistake surfaces in a check, they are the only proof of what was deducted and why.
The 303 done properly from here on
Carlos filed the supplementary return in October 2026, together with the one for the 2025 fuel costs, and adjusted the 2026 quarters to 50 %. The previous gestoría agreed to pay the surcharge and the cost of the correction without the need to go any further. It does not always turn out that way, and we do not promise it, but it does so a good deal more often when the claim arrives well documented and with an honest figure.
The guide to Modelo 303 for the self-employed explains which costs are deductible and within what limits, and the one on the article 27 surcharge lets you redo the calculation with your own dates.