Peter is British, retired and has lived in Marbella since 2019. Every year a gestoría (an administrative and tax agency) prepared his income tax return. In July 2026 he received a proposed assessment from the Agencia Tributaria, the Spanish tax agency, for 2023: the dividends from his portfolio at a London bank, around €8,400 a year, were missing, and on top of that the gestoría had applied a regional deduction to which he was not entitled. The proposal added up to €2,100 of tax, €190 of interest and a warning that a penalty procedure would follow. Peter had sent the gestoría all the statements from the English bank. Nobody put them in the return.
Peter's question had two parts: whether he has to pay for something that is someone else's fault, and how he claims it back from them. The first answer is yes: as far as the tax office is concerned, the return is his. The second is less obvious and we go through it below. Background on the obligations of individuals is on our self-employed in Spain page.
In the eyes of the tax office, the taxpayer is always the one obliged
Filing your income tax return through a professional, under a power of attorney or through an authorised filing agent (colaborador social), does not change who the taxpayer is. What the gestoría signed on Peter's behalf, Peter signed. If there is tax to pay, interest or a penalty, they are assessed in his name. The Agencia Tributaria takes no account of private arrangements between the taxpayer and their adviser.
That does not mean the adviser's mistake is irrelevant in the file. A penalty requires fault, at least negligence, and the Ley General Tributaria, the General Tax Act, excludes liability where due care has been taken, for example where someone acts on a reasonable interpretation of the rules. Having handed all the documents to the professional is an argument for maintaining that the taxpayer was not negligent. It is not automatic: the courts weigh each case, and an adviser's mistake does not always let the client off.
The three scenarios and the tool for each
| Situation | Tool | Deadline | What happens to the cost |
|---|---|---|---|
| You spot the mistake yourself, before the tax office, and more tax is due | Corrective self-assessment with the right result | As long as it is not time-barred (4 years) | Tax plus the surcharge under article 27; no penalty |
| You spot a mistake that made you pay too much | Corrective self-assessment asking for a refund | 4 years | Refund with late-payment interest in your favour |
| The tax office has already sent you a proposed assessment | Submissions (alegaciones) within the period it states | The one in the proposal, normally 10 working days | Tax, interest and a possible penalty |
Since Ley 13/2023, Modelo 100 is corrected with a single corrective self-assessment, whether the result goes up or down; before, there were two separate routes, the supplementary return and the request for rectification. How it is done in practice is explained in how to correct a return already filed.
Peter's sums
- Missing tax: €2,100, for the undeclared dividends and the wrongly applied deduction. He owed that amount in any case: with or without the mistake, he would have had to pay it in 2024.
- Late-payment interest: €190, for the time that money was not in the tax office's hands.
- Possible penalty: 50 % of the tax, €1,050. With acceptance (30 %), €735; with prompt payment as well (40 %), €441.
- Cost that would not have existed without the mistake: the penalty, if imposed, and the fees for putting it right.
Peter could no longer file a corrective return on his own initiative, because the proposal had already arrived. What he could do was make submissions against the penalty, providing the emails in which he sent the statements to the gestoría. If you have a similar case, tell us about it in the self-employed form. How to answer a proposal is explained in from proposal to assessment.
The wrongly applied regional deduction
Peter's second mistake is very common. Regional deductions have their own requirements on age, maximum income, residence in the region or supporting documents, and they change often. Applying them because the program offers them, without checking that they are met, is a common way of paying less in June and considerably more three years later. Here there is a legitimate question for the adviser: whether they checked the requirements before ticking the box or simply ticked it.
What can be claimed from the adviser, and what cannot
The route is civil: breach of the professional engagement. Article 1101 of the Código Civil, the Civil Code, requires anyone who fails to meet their obligations through wilful misconduct, negligence or delay to compensate the damage, and the personal action becomes time-barred after five years (article 1964.2 of the Civil Code).
What almost nobody separates properly is what counts as damage and what does not:
- The tax is not damage. Peter owed the €2,100 anyway.
- Late-payment interest compensates for his having had that money in his account for two years; claiming it from the adviser is debatable and depends on the case.
- The penalty usually is damage, if it would not have been imposed without the mistake.
- The surcharge on a late corrective return is too.
- The fees of the professional who corrects the mistake.
- The lost refund, if the mistake was in the tax office's favour and the four years to claim it have already gone by.
How the mistake is documented
What decides a claim is not who is right, but who can prove it. For Peter, the essentials were:
- The engagement letter, or the emails in which the gestoría agreed to prepare his return each year for a fee.
- The emails with the English bank statements attached, with their dates.
- The return as filed, which shows that the income does not appear.
- The proposal and, in due course, the assessment and the penalty, which quantify the loss.
With that, the usual step is a letter to the adviser describing the mistake and the amount and asking them to notify their professional liability insurer. Many professional bodies and associations require their members to hold that insurance. Whether the insurer pays cannot be guaranteed: it depends on the policy, its exclusions and how the case is assessed.
A draft return confirmed without questions, and other mistakes of omission
Many mistakes are not the adviser's but the draft return's. If the professional confirmed your draft without asking you about foreign income, rentals or sales, the mistake is one of omission, and the question is whether their engagement included reviewing that or only processing the return. That is why the engagement letter matters so much.
And a mistake in the return of a resident with assets abroad can drag others along with it: if dividends from a foreign bank were missing, perhaps Modelo 720 (the return declaring assets held abroad) for those accounts is missing too. It is worth looking at everything together, before the Agencia Tributaria does.
The deadline on a proposed assessment runs from notification, not from when the adviser replies. If you do not make submissions in time, the assessment will arrive anyway and the penalty will be harder to contest. Make the submissions yourself, or have another professional do it, and claim afterwards.
Peter made submissions with his emails to the gestoría and paid the tax and the interest to stop the interest building up. The outcome of the penalty procedure and of the claim against the gestoría remains to be seen: neither can be promised. What can no longer happen to him is the deadline running out without anyone acting. If your adviser's mistake was in the withholding summary rather than in the income tax return, we deal with it in my adviser got Modelo 190 wrong.