Sergio Pastor lives in Valencia and since 2024 has been letting a flat he inherited in Ruzafa to a couple. He did not declare that rent in his income tax return for 2024 or for 2025: he thought that, as he had a salary and few deductions, "Hacienda would cross-check it anyway" (Hacienda being the usual name for the Spanish tax office). In September 2026 a friend explains to him that it does not, and he decides to put things right before any letter arrives. He has worked out that it will come to about 5,600 € for 2024 and 6,100 € for 2025. He has about 6,000 € saved. His first idea is to phone the tax agency and ask for a deferral "for everything that is going to come out" before filing anything.
That call would be no use. And the order in which he does things is going to decide how much he pays in surcharges.
Why you cannot defer before declaring
Article 47.1.a) of the Reglamento General de Recaudación (the General Collection Regulations) declares a deferral application inadmissible when the debt has to be self-assessed and the self-assessment has not been filed before or together with the application. Until Sergio files the supplementary returns, there is no debt to defer.
And there is a second rule that fixes the moment: article 46.1.a) says that, for self-assessments filed late, the application is only treated as made in the voluntary period if it is filed together with the late self-assessment. If Sergio files today and applies for the deferral tomorrow, that debt will already be in the enforcement period, because article 161.1.b) of the Ley General Tributaria (the General Tax Law) starts the enforcement period on the day after a return is filed without payment.
The steps, with Sergio's dates
- Calculate before filing. Redo both returns with the rent and the deductible expenses, and know how much each one comes to.
- Calculate each year's surcharge, because it is not the same.
- Decide what is paid and what is deferred. This is where the saving lies that almost nobody sees.
- File each supplementary return with the payment option or with the option of acknowledging the debt and applying for deferral.
- Wait for the surcharge assessment, which the Agency notifies later, separately and with its own payment period.
Two years, two different surcharges
Article 27.2 of the General Tax Law sets the surcharge for filing without a prior request from the tax authorities: 1 % plus a further 1 % for each full month of delay, and 15 % from twelve months onwards, with late-payment interest from the day after those twelve months. It rules out penalties.
Assuming Sergio files on 25 September 2026:
| Tax year | End of the filing period | Delay | Surcharge | Surcharge amount | Interest |
|---|---|---|---|---|---|
| 2025 | End of June 2026 | Two full months | 3 % | 6,100 × 3 % = 183 € | No |
| 2024 | End of June 2025 | More than twelve months | 15 % | 5,600 × 15 % = 840 € | Yes, from the end of June 2026 |
At an assumed rate of 4 % a year, purely for the example, the interest for 2024 over about 87 days would be around 53 €.
The 25 % reduction and what deferral does to it
Article 27.5 of the same law reduces the surcharge by 25 % if two conditions are met:
- The whole surcharge is paid within the period opened by its assessment.
- The whole debt in the self-assessment is paid when it is filed, or is paid in the instalments of a deferral granted with a bank guarantee or surety insurance certificate and applied for on filing.
The practical consequence is very specific: a deferral without a guarantee, even if it is granted without difficulty because the debt is below 50,000 €, means losing the 25 % reduction in the surcharge on that debt.
For an ordinary debt, deferring without a guarantee only costs interest. For a late self-assessment it also costs a quarter of the surcharge. It is worth adding that up before choosing between paying, deferring with a bank guarantee or deferring without one.
The saving that depends on the order
Sergio has 6,000 € and two debts: 5,600 € and 6,100 €. He can only pay one of them outright. Which one?
If he pays 2025 and defers 2024 without a guarantee:
- 2025 surcharge with the reduction: 183 × 0.75 = 137.25 €.
- 2024 surcharge without the reduction: 840 €.
- Total in surcharges: 977.25 €, plus the interest on the deferral.
If he pays 2024 and defers 2025 without a guarantee:
- 2024 surcharge with the reduction: 840 × 0.75 = 630 €.
- 2025 surcharge without the reduction: 183 €.
- Total in surcharges: 813 €, plus the interest on the deferral.
With the same money and the same debt, the second option saves about 164 €. The general rule is simple: pay outright the year with the highest surcharge and defer the one with the lowest. In cases with more years or larger figures, the difference grows.
For large amounts it is also worth comparing with a bank guarantee: if the cost of the guarantee is less than a quarter of the surcharge that would be saved, it pays off. We deal with this in how much can be deferred without a guarantee.
The trap of the second letter
The surcharge assessment arrives weeks or months later, when the supplementary return already seems a closed matter. It has its own payment period, the one in article 62.2 of the law. If it is not paid within that period, the 25 % reduction is lost even if the tax itself was paid on time, and article 27.5 itself allows the reduced amount to be claimed without further formality.
That surcharge can also be deferred, but then it is not paid "within the period" either and the reduction is lost. For Sergio, the sensible thing is to set aside from the start the 630 € of the 2024 surcharge and have it available when the letter arrives.
If you are going to put several years right and would like us to work out what is best paid and what is best deferred, you can send us the returns and what remains to be declared through the deferral form. We cannot guarantee that the deferral will be granted, but we can make sure the order of filing does not cost you more surcharge than necessary.
What not to do
- File without paying and without applying. Article 27.3 warns that, in that case, the enforcement-period surcharges and interest on the tax are added to the late-filing surcharge.
- Wait until you have all the money. As long as you do not file, the surcharge goes up one point a month until twelve months, and after that it stays at 15 % but interest starts.
- Wait for a letter to arrive. If the Agency starts any action of which the taxpayer has formal knowledge, it is no longer a voluntary correction and the surcharge is replaced by a possible penalty. The guide on what counts as a prior request explains it.
- Count on the 60/40 split for the income tax return. The interest-free split for IRPF does not apply to supplementary returns, as we explain in deferring your income tax return.
The full calculation of the surcharge is in the guide on the article 27 surcharge, and the mechanics of putting past years right and deferring at the same time in deferring what comes out of putting past years right. If several tax years are involved, it is also worth reading putting several years right at once.
The order between tax years, what is paid outright and what is deferred, is what we decide at Salama Tax before the first supplementary return is filed.