Carmen and Álvaro Pineda inherited a flat in Cádiz from their mother and sold it in March 2024, half each. Each made a gain that meant about 2,000 € of tax on their 2024 income tax return, and neither declared it: the notary told them that the plusvalía municipal, the local tax on the increase in land value, had already been paid, and both understood there was nothing more to do. In August 2026 Carmen mentions it to a colleague at work, realises the mistake and files a supplementary return on 20 September. Álvaro prefers to wait. In January 2027 he receives a request and, two months later, an assessment with a proposed penalty.
Same mistake, same tax, same date of sale. What they pay is very different, because each has ended up in a different box of the law.
Three pieces with three different reasons
| Surcharge under article 27 | Late-payment interest | Penalty | |
|---|---|---|---|
| Why it arises | You file late without a prior request | The money was out of the Treasury | An infringement involving fault |
| Nature | Ancillary charge, not a penalty | Ancillary charge, compensatory | Punitive |
| How much | 1 % plus 1 point for each complete month; 15 % from twelve months | The legal rate for the period, on the tax | From 50 % for minor infringements up to 150 % |
| What reduces it | 25 % if paid within the periods in article 27.5 | Nothing | 30 % for agreeing and 40 % for prompt payment |
| Requires fault to be proved | No | No | Yes |
| Stays on record | No | No | Yes, for four years |
The surcharge replaces the penalty: article 27.2 says that the surcharge "shall exclude penalties". Interest, on the other hand, goes with either of the two when the delay is long enough.
Carmen's figures
Her 2024 income tax return had to be filed by 30 June 2025. By 20 September 2026 more than twelve months have passed. With an interest rate assumed to be 4 % a year, purely for the example:
- 15 % surcharge on 2,000 €: 300 €.
- 25 % reduction under article 27.5, because she pays the tax on filing and will pay the surcharge within the period opened by its notification: it comes down to 225 €.
- Late-payment interest only from the day after the twelve months, 1 July 2026, until 20 September: 82 days, about 17.97 €.
- Cost on top of the tax: 242.97 €.
Álvaro's figures
The request gets there before he does. From that moment he can no longer file with a surcharge: article 27.1 treats as a prior request any notified administrative action aimed at correcting that debt. The assessment is issued to him in March 2027.
- Late-payment interest from 1 July 2025 until the assessment, about twenty months: around 133.33 €.
- Penalty under article 191. The base is below 3,000 €, so the infringement is minor and the fine is 50 %: 1,000 €.
- If he agrees with the assessment, article 188.1.b) reduces the penalty by 30 %: 700 €.
- If he also pays on time and does not appeal, article 188.3 applies a further 40 % to what remains: 420 €.
- Cost on top of the tax, in the best case: 553.33 €. If he appeals and loses: 1,133.33 €.
| Carmen | Álvaro, agreeing and paying | Álvaro, appealing unsuccessfully | |
|---|---|---|---|
| Tax | 2,000 € | 2,000 € | 2,000 € |
| Surcharge | 225 € | 0 € | 0 € |
| Interest | 17.97 € | 133.33 € | 133.33 € |
| Penalty | 0 € | 420 € | 1,000 € |
| Total | 2,242.97 € | 2,553.33 € | 3,133.33 € |
The discount on the surcharge does not depend on appealing
A common misunderstanding is to think that the surcharge loses its reduction if it is appealed, just like the penalty. That is not so. Article 27.5 requires two payments: that of the debt, on filing or within a deferral granted with a bank guarantee or surety insurance, and that of the surcharge, within the period opened by its assessment. It makes no mention of appeals. If either of those payments is missed, the reduction is claimed back with no further formality.
With the penalty the opposite happens. The reduction for agreeing is lost if the correction of the tax is appealed, under article 188.2.b), and the prompt-payment reduction is lost if the assessment or the penalty is appealed, under article 188.3.
In Álvaro's example, appealing and losing costs 580 € more than agreeing and paying. If his chances of winning are high, it is worth it; if they are low, it is not. And there is an added difficulty: appealing the penalty forces a choice about whether to appeal the tax as well. That decision is taken with figures in front of you and with the decision read in full, not on principle.
Where fault comes into a penalty
The penalty is the only one of the three that needs fault. The Administration has to explain why the conduct was at least negligent, and article 179.2.d) excludes liability where the necessary diligence was shown, for example by acting on a reasonable interpretation of the rule.
In Álvaro's case the defence would be difficult. Confusing the local land value tax with income tax is understandable, but it is not a reasonable interpretation of an unclear rule: taxing the gain in the income tax return is a clear rule. If the mistake had been about how to calculate the acquisition value of an inherited asset, where the criteria are disputed, the argument would have more room.
The trace each one leaves
The surcharge leaves no record. The penalty does. Article 187.1.a) raises the minimum penalty for a later infringement of the same nature committed within the four years after the earlier one became final: five points if the first was minor, fifteen if it was serious and twenty-five if it was very serious. The infringements in articles 191, 192 and 193 all count as being of the same nature.
The aggravating factor operates on infringements that are graded, the serious and very serious ones; a minor one has a fixed percentage. If in 2028 Álvaro commits another infringement under article 191 that turns out to be serious, his penalty will not start from 50 % but from 55 %. Carmen starts from zero.
If you have a mistake of this kind and nothing has reached you yet, the voluntary correction form lets us work out the surcharge, the interest and the difference from the penalty scenario before you file.
Interest, which is not negotiable
Late-payment interest is the piece that is argued about least and misunderstood most. It neither punishes nor rewards: it compensates for time. Article 26.1 says that it requires neither prior demand nor culpable delay. Article 26.6 sets it at the legal rate of interest plus 25 %, unless the Budget Act sets a different one.
With the surcharge, interest only appears when more than twelve months have passed, and only for the time beyond those twelve months. In an assessment by the tax agency, it runs from the end of the filing period for the return. That is why Álvaro pays more interest than Carmen even though the debt is the same.
What decides which box you fall into
Almost always it is a single circumstance: who moves first. If the taxpayer files before anything is notified to them, a surcharge. If the Administration notifies first, a penalty. The exact boundary is in if I go first, can I still be penalised?, and the guide to surcharge versus penalty has more examples. To work out your own surcharge month by month, there is the surcharge calculator.
Getting in first, with the cost worked out and the years reviewed, is the basis of Salama Tax's voluntary correction service.