A self-assessment may not be the subject of the special review procedure for acts that are null as of right

In judgment no. 350/2026 of 20 March (Contentious-Administrative Chamber, Second Section, cassation appeal no. 422/2024, rapporteur Mr Isaac Merino Jara), the Spanish Supreme Court reiterates a doctrine of real importance for the taxpayer’s procedural strategy: a tax self-assessment is not an administrative act and, therefore, may not be subject to the special review procedure for acts null as of right (nulidad de pleno derecho) provided for in article 217 of the General Tax Act (LGT).

The facts are common in estates with an international element. The taxpayer’s mother, not a Spanish tax resident, died in May 2012. The heir filed his self-assessment of the Inheritance and Gift Tax (ISD) in February 2013, in accordance with the rules in force at the time, which reserved for heirs of non-resident decedents a more onerous tax treatment than that applicable to heirs of decedents resident in Spain.

Some eighteen months later, on 3 September 2014, the Court of Justice of the European Union delivered the judgment Commission v. Spain (case C-127/12). In it, the CJEU held that the ISD regime applicable to non-residents infringed the free movement of capital recognised in the Treaty on the Functioning of the EU.

In practice, that judgment allowed heirs who had paid tax in Spain under the previous rules to claim a refund of the excess paid, since they had been taxed under a regime contrary to EU law.

The taxpayer in this case, however, did not react until November 2020. By then, his self-assessment had become final by the lapse of the four-year statute of limitations. Rather than using the ordinary rectification procedure of article 120.3 of the LGT —the natural route where a self-assessment prejudices the legitimate interests of the taxpayer— he sought a declaration of nullity as of right under article 217.1.a) of the LGT, on the grounds of breach of the principle of equality and of EU law.

The AEAT refused to admit the request and the Central Administrative Court upheld that refusal, but the Audiencia Nacional, in a judgment of 27 June 2023, allowed the taxpayer’s appeal. It was the State Attorney who appealed in cassation. The Supreme Court quashes the Audiencia Nacional judgment and confirms the refusal to admit the request for ex officio review.

The Supreme Court rejects the claim on a threshold ground, prior to the merits. Article 217 of the LGT governs a special review procedure for administrative acts. And the self-assessment, according to the Supreme Court’s own settled case law, is not an administrative act.

The self-assessment is an act of cooperation by the taxpayer in the application of taxes. The taxpayer declares the facts, characterises the transaction and quantifies the liability, without prior pronouncement by the Administration. To react against it, the legal order provides its own channel: the request for rectification under article 120.3 of the LGT and, where applicable, the refund of undue payments under article 32 of the LGT.

The Chamber adds a nuance worth keeping in mind. The tax Administration’s failure to act on the self-assessment within the statute of limitations does not convert it into a presumed administrative act. Administrative silence operates only where the Administration has a legal duty to pronounce, which is not the case in respect of a self-assessment that has not been the subject of a request for rectification.

As to the possible breach of EU law, the judgment holds that the ordinary four-year statute of limitations is reasonable and does not render impossible or excessively difficult the exercise of rights derived from EU law. The interested party had, accordingly, an effective margin of several years —between the Commission v. Spain judgment of September 2014 and the lapse by prescription of his own self-assessment— to seek rectification and, nevertheless, did not do so.

As to the principle of equality under article 14 of the Spanish Constitution, the Spanish Supreme Court relies on Order 116/2019 of the Constitutional Court. The situation of a taxpayer under a self-assessment regime and that of a taxpayer under an administrative assessment regime are not comparable: in the first case there is no prior administrative act but a private act of declaration; in the second there is. Unequal treatment cannot therefore be predicated between situations that, by their very legal configuration, are different.

In our view, the doctrine of the Spanish Supreme Court is coherent with the logic of the system. The self-assessment is a mechanism for the mass application of the tax which rests on the taxpayer’s cooperation. Its review is entrusted to the interested party through a channel designed for that purpose —article 120.3 of the LGT—, subject to the general statute of limitations. To allow it to be challenged through article 217 of the LGT years after filing would open a breach in the principle of legal certainty that neither EU law nor the constitutional principle of equality requires.

The practical consequence is serious for taxpayers who relied on a potential reopening through the nullity route. A self-assessment that has become final by prescription is not reopened through the extraordinary channel of article 217 of the LGT, not even where a later CJEU judgment declares contrary to EU law the rule under which the tax was paid.

In comparable cases, the prudent course is to act within the four-year limitation period by seeking rectification of the self-assessment under article 120.3 of the LGT. A State liability claim for legislative acts may also be available, a route the judgment itself mentions, although subject to its own requirements and time limits (article 32 of Law 40/2015), whose compatibility with EU law has been disputed.

In conclusion, what this judgment of the Spanish Supreme Court makes clear is that the tax self-assessment operates under a procedural regime of its own, distinct from that of administrative acts. Where it is considered contrary to law, the channel is the rectification of article 120.3 of the LGT, exercised within the ordinary statute of limitations. The extraordinary route of nullity as of right under article 217 of the LGT does not open a second chance once that period has elapsed.