Hugo Sanz, a lecturer at the University of Salamanca, sold his flat next to the Plaza Mayor, the city's main square, in June 2025. He declared the sale in his 2025 income tax return, filed in June 2026, with the intention to reinvest: the gain was 48,000 € and the amount obtained 160,000 €. He planned to buy a house in Villamayor, just outside Salamanca. In September 2026 he is awarded a four-year research post at another university, decides to rent there and puts the purchase on hold. The gain he declared exempt will no longer be exempt. He wants to know what he has to file, when, and how much the change of plans will cost him.
What the Regulations say
Article 41.5 of the Regulations on IRPF (Spanish personal income tax) contains the complete rule. Failure to meet any of the conditions of the exemption means that the corresponding part of the gain is taxed. In that case, the taxpayer "shall allocate the non-exempt part of the capital gain to the year in which it was obtained, filing a supplementary return, including late-payment interest". And that supplementary return is filed "within the period between the date on which the failure occurs and the end of the regulatory filing period for the tax period in which that failure occurs".
Three practical consequences:
- The gain is not declared in the year in which the decision not to reinvest is taken, but in the year of the sale. For Hugo, in 2025.
- The tax that would have been due then is paid, plus late-payment interest for the time that has passed.
- If it is filed within the window in article 41.5, the supplementary return is on time and carries no surcharge for late filing.
When the failure occurs
Hugo has two possible dates. One is June 2027, when the two years from the sale expire without any reinvestment: at that point the failure is objective. The other is September 2026, when he finally decides not to buy. The Regulations do not require him to wait until the end of the period, and nothing prevents him from putting things right earlier if his decision is firm.
| Milestone | Date for Hugo |
|---|---|
| Sale of the flat | June 2025 |
| End of the filing campaign for the 2025 return | June 2026 |
| Decision not to buy | September 2026 |
| End of the reinvestment period | June 2027 |
| Last day for the supplementary return if the failure occurs in 2027 | End of the filing campaign for the 2027 return, around mid-2028 |
If Hugo waits until the limit, he will have almost two more years of accumulated interest. If he files the supplementary return in autumn 2026, he will pay interest for a few months.
How much is taxed and how it is calculated
The gain Hugo declared exempt in 2025 becomes taxable in the 2025 savings base. The supplementary return is calculated as follows:
- 2025 gain declared exempt: 48,000 €.
- Reinvestment made: 0 €.
- Gain now taxed: 48,000 €.
- The 2025 return is redone, including that gain in the savings base.
- The difference between the new tax figure and the one in the original return is what is paid.
- Late-payment interest is calculated on that difference from the end of the filing period for 2025 to the day on which the supplementary return is filed.
The tax depends on Hugo's other income in 2025 and on the savings scale, so we do not give it here; the late-payment interest rate is set each year by the budget law. What can be said is that the cost of waiting grows with each month.
If Hugo had managed to invest part, for example 100,000 € in a home he did live in, only the part not covered would be taxed: the exempt part would be 48,000 × 100,000 ÷ 160,000 = 30,000 €, and the supplementary return would include 18,000 €. The proportion is explained in if I reinvest only part, how much is exempt?.
What happens if the window is allowed to pass
If Hugo does not file the supplementary return within the period in article 41.5, filing it later is late filing. Done before any request from Hacienda, as the Spanish tax office is commonly called, it carries the surcharge in article 27 of the General Taxation Law: 1 % plus another 1 % for each full month of delay, and 15 % with interest once more than twelve months have passed. The surcharge, on the other hand, rules out a penalty.
If it is Hacienda that detects it first, for example when reviewing the 2025 return and finding that no purchase appears, the correction will be made in a verification procedure, with interest, and with the possibility of separate penalty proceedings. That is why getting in first is the option that costs least: the same debt, less interest and no surcharge or penalty. The difference between a surcharge and a penalty is explained in what is the difference between a surcharge and a penalty.
Someone who records the intention to reinvest leaves a record in their return that they have a gain still to be confirmed. It is a piece of information Hacienda can review when the period expires. Not putting things right in time is not a discreet option: it usually ends in a request for information, and what would have been a supplementary return with interest can turn into an assessment with a penalty. We cannot predict when each file will be reviewed, but we can say that a review is possible throughout the limitation period.
If the reason is a forced move
Hugo's case has a nuance. His decision not to buy stems from a change of job. That does not save the exemption on the 2025 sale: the cause that forces a change of address serves to waive the three years of residence, but it does not replace reinvestment. If he had bought the house in Villamayor, lived in it for a few months and then moved away for the new post, the situation would be different, because then the transfer for work could justify not completing the three years in the new home. We explain this in I have not lived in the house for three years.
Nor does it help to reinvest in a home that is not going to be the main home. If Hugo bought in Villamayor to let it while he lives elsewhere, that purchase would not fulfil the purpose of the exemption and the supplementary return would still be necessary.
How the supplementary return is prepared
The 2025 supplementary return is made on the basis of the original return: the section on the sale is changed so that the exemption is no longer applied, in whole or in part, the new tax is calculated and the interest is added. It is best done with the original return in front of you and with the figures from the calculation of the amount obtained, so as not to change anything else. How a return is corrected in general is explained in how to correct a return already filed.
If you are in Hugo's situation, send us through the reinvestment form the return for the year of the sale and the date on which you decided not to buy; with that, the supplementary return and the interest up to the planned filing date can be calculated.
Before giving up altogether
It is worth checking whether any reinvestment is still possible within the time limit. A purchase in the two years following the sale, even for a smaller amount, saves a proportional part of the exemption. And if the new home is bought with borrowed money, it is worth checking which payments would fall within the time limit. The dates of the window are explained in the two years: from when and until when, and the mechanics of the calculation in the guide on calculating the amount to reinvest.
Correcting a reinvestment that never happens, with the calculation of the supplementary return and its interest, is part of the Salama Tax service for selling your main home.