Ana and her brother Luis inherited from their mother, who died in Valencia on 2 August 2025, a flat in the Ruzafa district and a savings account. They gave the inheritance tax to the gestoría (the local firm that handles tax paperwork) the family had always used. The gestoría declared the flat at 180,000 euros, an estimated market value, and filed the two Modelo 650 returns on time. In July 2026, while preparing to sell the flat, the estate agent tells them that the Catastro's reference value for that property was 240,000 euros. And they wonder whether that is a problem.
It is. Since 2022, the valor de referencia (the official reference value set by the Catastro, the Spanish property cadastre) is the minimum base at which properties are declared for inheritance tax. Declaring below it is a mistake the tax administration detects almost automatically, because the figure is its own.
What the rules say about the value of property
Law 11/2021 on measures to prevent and combat tax fraud amended the Inheritance and Gift Tax Law so that the value of property is, at least, its reference value at the date the tax accrues, which in an inheritance is the date of death. If a higher value is declared, the declared one is taken; if less is declared, the administration applies the reference value.
The reference value is looked up on the Catastro's electronic office with the cadastral reference, for any date since 2022. It is not a figure that has to be estimated, but one that has to be looked up. That is why a 650 with a property below its reference value is almost always a mistake by whoever prepared the return. More detail on valuing each asset in valuing assets in an inheritance.
What the gestoría's mistake amounts to
The difference between what was declared and the reference value is 60,000 euros, 30,000 euros for each sibling. Suppose, for the purposes of the example, that this additional slice is taxed at an effective rate of 10% after applying the regional rules, the reductions and the coefficients. It is only an assumption: in regions with high reliefs for children the real tax can be much lower. The exact figure depends on the rest of the estate and on the rules in force at the date of death:
| Item | Per sibling | If corrected now, without a request | If the administration gets there first |
|---|---|---|---|
| Additional base | 30,000 euros | 30,000 euros | 30,000 euros |
| Additional tax (example at 10%) | 3,000 euros | 3,000 euros | 3,000 euros |
| Surcharge or penalty | — | Article 27 recargo: 9% if filed in mid-October 2026 (8 full months since 3-2-2026) = 270 euros; with the reduction, 202.50 euros | Possible article 191 penalty: minimum 50% = 1,500 euros, with its reductions |
| Late-payment interest | — | No, below twelve months | Yes |
The deadline for the two 650s ended on 2 February 2026, six months after the death. Correcting now, with a supplementary self-assessment, each sibling pays 3,000 euros of tax and about 200 euros of recargo (the surcharge for filing late unprompted). If they wait for the Valencian administration to review it, which is the most likely outcome with a cadastral figure involved, the bill can triple.
Who answers to Hacienda and who answers to the siblings
Before the administration, the taxpayers are Ana and Luis. They signed the self-assessment or it was filed in their name, and the tax, the surcharge or the penalty are required from them. The fact that the gestoría made a mistake does not transfer the debt. It may be relevant when assessing fault in penalty proceedings, but it is not something to count on in advance.
The relationship with the gestoría is a contract for services, and whatever the gestoría has to answer for is claimed through the civil courts. Here the division is clear:
- The additional tax cannot be claimed. The 3,000 euros per sibling were owed from the start: the mistake did not create them, it only postponed them.
- The surcharge can be, because it is a direct consequence of filing incorrectly.
- A penalty, if one came, can be too, provided the mistake was the professional's and not in the information the siblings gave.
- The fees for the correction, likewise, as consequential loss.
If you are in a similar situation and want to know what has to be corrected and what it costs, the inheritance and gift form collects what is needed to review it.
The value at which a property is declared in the inheritance is the one that will later be used as the acquisition value when the heirs sell it. Declaring it low does not just make inheritance tax cheaper: it makes the capital gain in income tax more expensive on the day of the sale. Correcting the 650 to the reference value therefore has a positive effect on Ana and Luis's income tax when they sell the Ruzafa flat.
Other gestoría mistakes in inheritance tax that we see often
Letting the extension slip
If the gestoría received the instruction in the third month and the documents were not ready, the right move was to request the extension before the fifth month. Not requesting it and filing late generates a surcharge that is a direct consequence of that omission.
Filing in the wrong region
The competent region is that of the deceased's habitual residence, not the heir's or the property's. A self-assessment filed with the wrong administration does not meet the obligation before the right one, and the correction may come after the deadline. The full table is in the ISD competence table.
Household contents miscalculated
The law presumes that the household contents (the ajuar doméstico) are worth 3% of the net estate, unless proven otherwise. Applying it to all the assets without more, when it is arguable which assets belong in that base, can mean paying too much. It is an issue on which court doctrine has gradually narrowed the calculation, and it is worth reviewing in each case.
Not applying a reduction that was due
Regional reductions for kinship, for the main home or for the family business have formal requirements. Forgetting one means paying too much. That is corrected by requesting rectification of the self-assessment within four years of the end of the deadline, with a refund and interest if it succeeds.
The step before: checking the other figures
Before filing the supplementary return, it is worth reviewing the rest of the return with the same magnifying glass. If the flat was wrongly valued, the account balance may be too, since it must be taken at the date of death and not at the date of the certificate, or some deductible expense may be missing, such as the funeral or the mother's outstanding debts. A supplementary return that corrects one mistake and leaves others open means filing another one later.
How to document the claim against the gestoría
Ana and Luis need three things: proof of the engagement, whether an engagement letter, a quote or invoices; proof of what they handed over, in particular whether they gave the flat's cadastral reference, which is what made it possible to look up the reference value; and the amount of the loss, which is only known once the correction has been made. With that, the orderly step is a formal demand by a means that leaves proof of delivery, asking for the loss to be paid and for the gestoría to notify its professional liability insurer. There is no guarantee they will accept, and personal actions have five years under article 1964 of the Código Civil (the Spanish Civil Code). But the sooner the correction is made with the administration, the smaller the loss and the easier it is to prove.
Common doubts when an adviser has got Modelo 650 wrong
If the mistake was my adviser's, am I still liable?
Before Hacienda, yes: in Modelo 650 the taxpayer is you, and the debt is claimed from you. What you can do is argue that there was no fault, which is what can bring down the penalty, not the debt, and, on a completely different level, claim against the professional or their insurer. They are two separate things and they follow separate routes.
Can I ask for more time?
Yes: an extension of another six months, but it has to be requested within the first five. After that point it is no longer possible, and it is one of the deadlines most often let slip.