Unjustified capital gains: recent case law of the Supreme Court
Unjustified Capital Gains constitute one of the most common grounds for adjustment in Personal Income Tax (IRPF) where the Tax Authorities identify undeclared assets or rights in the course of a review or inspection procedure.
Throughout this post, we shall examine the most recent judgments of 27 November 2025 delivered by the Supreme Court (appeals nos. 5514/2023 and 2028/2023), in which the Court reaffirms the doctrine concerning the burden of proof and clarifies what the taxpayer must substantiate in order to rebut the attribution made during a review or inspection procedure.
What is regarded as a capital gain?
Pursuant to Article 33 of the Ley del Impuesto sobre la Renta de las Personas Físicas (hereinafter, the “LIRPF”), a capital gain shall, as a general rule, be deemed to arise where the following requirements are satisfied:
- That there is a variation in the value of the taxpayer’s estate (being the difference between the disposal value and the acquisition value of the relevant asset).
- That there is an alteration in the composition of the taxpayer’s estate (such as the transfer, gift or exchange of an asset, including, inter alia, the sale of immovable property, the transfer of shareholdings, or the disposal of investment funds).
However, the legislation governing Personal Income Tax (IRPF) provides for a specific category: Unjustified Capital Gains.
What are unjustified capital gains?
The concept of unjustified Capital Gains is set out in Article 39 of the Personal Income Tax Law (LIRPF).
This provision establishes that “assets or rights whose possession, disclosure or acquisition does not correspond to the income or estate declared by the taxpayer shall be regarded as unjustified capital gains.”
An unjustified Capital Gain therefore refers to an increase in wealth which is not consistent with the income declared or with the taxpayer’s economic activity.
In practice, this arises where the Tax Authorities, in the course of a review or inspection procedure, identify:
- The receipt of undeclared income (such as rental income derived from the letting of immovable property).
- Increases in wealth that are inconsistent with the income declared.
- Undeclared assets or rights, as may occur in certain cases involving individuals who are tax resident in Spain and hold assets or rights abroad, and who fail to declare properly their disposal for Personal Income Tax purposes.
- Banking transactions lacking supporting documentation, as well as unsubstantiated gifts or inheritances.
Likewise, one of the common areas of adjustment concerns transactions between a partner and a company where these have not been properly documented. For example, where a shareholder receives transfers from the company which do not correspond to employment income, dividends, or the repayment of duly formalised loans.
In essence, this type of capital gain arises from a statutory presumption of an unexplained increase in wealth, the decisive factor being the absence of substantiation as to the origin of the asset or right in question.
Tax particularities of unjustified capital gains
Personal Income Tax (IRPF) is a dual tax which levies different categories of income (employment income, rental income, dividends, disposals of assets, etc.) and classifies them as follows:
- General Tax Base
- Savings Tax Base
This classification is significant because the top marginal rate applicable to the general scale may reach 49%, whereas the maximum rate applicable to the savings scale may be set at 30%.
As a general rule:
- Capital gains arising from a disposal are included in the savings tax base.
- Capital gains which do not arise from a disposal are included in the general tax base.
However, Article 39 of the Personal Income Tax Law (LIRPF) expressly provides that unjustified Capital Gains shall be included in the general taxable base of the tax period in which they are discovered.
This entails that, even where the underlying origin may in substance be linked to the disposal of an asset, the Tax Authorities may allocate such gains to the general tax base, the presumption of undeclared income prevailing over the intrinsic nature of the income concerned.
A common scenario is the failure to properly document loans between a partner and a company. Where a shareholder advances funds to the company and the company subsequently repays those amounts without sufficient documentary evidence, such repayment may be characterised as an unjustified Capital Gain and included in the general tax base.
Accordingly, the burden of proof rests with the taxpayer, who must substantiate the provenance of the funds in order to prevent their inclusion in the general taxable base.
How can an unjustified capital gain be rebutted?
The recent judgments of 27 November 2025 delivered by the Supreme Court (appeals nos. 5514/2023 and 2028/2023) clearly set out the requirements for rebutting this type of tax adjustment.
The Supreme Court makes clear that general or unsubstantiated assertions are insufficient. In order to rebut the characterisation as an unjustified Capital Gain, the taxpayer must demonstrate:
- The provenance of the assets or rights, identifying the means by which they were transferred or acquired.
- From whom they derive, by identifying the transferor.
- The reason for the transfer, by evidencing the legal transaction underpinning the operation.
In short, it is essential to substantiate the origin or source of the assets in question and the specific legal transaction by virtue of which the asset or right was acquired.
In a context of increasing information exchange, enhanced banking oversight and the prevention of tax evasion, risk mitigation depends upon properly formalising transactions and ensuring consistency between financial movements, accounting records and tax returns. As the Supreme Court has emphasised, the key issue is not merely that the origin be lawful, but that it be capable of being proven.
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