Spanish Constitutional Court STC 37/2026: When Does Inheritance Tax Accrue if Paternity Is Judicially Recognised Years After the Father's Death?

Analysis of Spanish Constitutional Court Judgment 37/2026 of 25 May (amparo 2593-2024, BOE-A-2026-13749): Inheritance Tax accrues irrevocably on the date of the deceased's death, even where extramarital paternity is judicially recognised years later and even when that prevents the heir from claiming later regional reliefs (such as the Canary Islands 99.9% rebate). Dissenting opinion by the reporting judge himself. Download the full BOE judgment.

The real-life case: one inheritance, two generations, a 99.9% rebate at stake

The Second Chamber of the Spanish Constitutional Court has resolved the following very real situation in its Judgment 37/2026 of 25 May ([BOE-A-2026-13749](https://www.boe.es/diario_boe/txt.php?id=BOE-A-2026-13749), amparo 2593-2024):

  • October 2006: a man dies in the Canary Islands without ever having formally recognised one of his biological children.
  • His sister, sole heir under the will, files the Inheritance and Gift Tax (ISD) return in April 2007.
  • The extramarital son, excluded from the will, starts civil paternity proceedings in 2007.
  • In 2008 the Court of First Instance n.º 12 of Las Palmas declares paternity proven. The Provincial Court confirms it in November 2009.
  • In the meantime, January 2008: the famous Canary Islands 99.9% rebate on Inheritance Tax for descendants (Groups I and II) enters into force —a relief that did not exist in 2006 when the father died.
  • The judicially recognised son asks to apply the 99.9% rebate to his share. The Canary Islands tax administration refuses, applying only the kinship reduction in force in 2006.

> The legal question: when does Inheritance Tax accrue when a child is judicially recognised years after the father's death? On the date of death (no rebate) or on the date of the final paternity judgment (with rebate)?

The Constitutional Court has had the final word: the date of death prevails. With a powerful dissenting opinion by the reporting judge himself.

1. Legal framework: Article 24 LISD and the strength of the accrual date

Article 24.1 of Law 29/1987 on the Spanish Inheritance and Gift Tax (LISD) is crystal clear:

> *"In acquisitions by reason of death… the tax shall accrue on the day the deceased dies."*

Article 24.3 LISD adds a single exception: when the effectiveness of the acquisition is suspended by a condition, term, trust or analogous limitation, accrual shifts to the day those limitations disappear. And Article 10.2 of the ISD Regulation clarifies that, once the inheritance is accepted, its effects retroact to the moment of death.

The accrual date is the exact moment when the tax obligation is born and, with it, the following essential elements crystallise:

  • The applicable legislation (national and regional).
  • Reductions on the taxable base.
  • Tax rates, coefficients and rebates.
  • The valuation of assets.

> That is why accrual is not a technicality: it defines how much you pay.