Facts

The testator B. née C. deceased (born 11 May 1942, died 12 December 2022) appointed the taxpayer A.A. (born 2 March 1963) as heir with a share of 50 % in her last will dated 8 April 2022. The taxpayer is not related to the testator under civil status law; his father is unknown in the register (entry: paternity unknown).

The taxpayer claims to be the biological son of the deceased Catholic priest B.C. (brother of the testator). As evidence, he submitted a DNA report from the Institute of Legal Medicine at the University of Zurich (12 June 2023) establishing a 99.999 % probability of paternal relationship between him and D.C. (nephew of the testator). He also relied on a witness statement from his aunt C.A. née D., who confirmed his descent from priest B.C.

The decedent’s place of residence municipality assessed the estate at CHF 3,872,960 and levied inheritance tax of 40 % (basic rate 20 % + surcharge 100 %) on the taxpayer’s share (CHF 1,936,480). The taxpayer appealed the assessment with a notice of objection dated 31 January 2024 but was unsuccessful. In parallel, he brought an action for a declaration of paternity against the municipal council of X./ZH, which was dismissed by the District Court (21 November 2023) and the Higher Court of Zurich (15 January 2024). The Lucerne Cantonal Court confirmed the assessment in a judgment dated 14 January 2025.

The taxpayer ultimately filed an appeal with the Federal Supreme Court and requested application of the reduced tax rate of 12 % (basic rate 6 % + surcharge 6 %) for the parental line or remission for reassessment.

Considerations

The Federal Supreme Court first examines the interpretation of the cantonal inheritance tax law (§ 3 Tax Act/LU), in particular whether the taxpayer can be assigned to the parental line (second parentel). The decisive factor is the reference to the civil-law concept of relationship under the CC (arts. 457 et seq. CC), since the cantonal tax law explicitly refers to civil-law concepts. A purely biological approach is not sufficient to establish a civil-law relationship of kinship. The taxpayer was unable to establish a legal parent-child relationship with priest B.C. either by recognition or by judicial determination, so he does not belong to the second parentel. The lower court was therefore correct to apply the basic rate of 20 %.

The taxpayer argues that the supplementary provision of § 3 para. 2 Tax Act/LU (illegitimate blood relatives) is applicable. This provision extends the basic rate to illegitimate but entitled blood relatives. However, this requires that the blood relationship be proven and the entitlement to inherit be clarified. The lower court did not examine this issue, as it focused on the civil court’s dismissal of the paternity action. The Federal Supreme Court clarifies that the supplementary provision constitutes an independent cantonal rule requiring the tax authorities to clarify the blood relationship and entitlement to inherit as a preliminary question. A DNA report and witness statement are sufficient as evidence, provided the tax authorities assess these means of evidence and, if necessary, obtain an expert opinion.

Entitlement to inherit within the meaning of the supplementary provision is not necessarily limited to statutory succession. A testamentary appointment as heir may also qualify as e…