Belgium Issues a Consultation on the Pillar Two IIR Top-up Tax Return

On March 19, 2026 Belgium issued a public consultation on the IIR top-up tax return. The FPS Finance is asking in-scope groups to comment, by April 3, 2026, on draft IIR return forms for assessment years 2024 and 2025 and on the accompanying explanatory notes. 

Belgium’s Pillar Two regime was enacted by the Law of 19 December 2023, which transposed Directive (EU) 2022/2523 and introduced three domestic charges: the domestic top-up tax, the IIR top-up tax and the UTPR top-up tax. The amending law of 12 May 2024 then inserted article 57/1, expressly requiring a form on which the Belgian amount of IIR and UTPR due is stated. The current consultation is therefore not just about polishing forms; it is about the legal instrument through which Belgium will assess and collect the IIR.

The statutory framework is already quite demanding. Under articles 53 to 57 of the 19 December 2023 law, each Belgian constituent entity must in principle file an annual IIR/UTPR return, although a designated local entity may file on behalf of others and a Belgian filing exemption exists where the ultimate parent entity or designated filing entity files in a jurisdiction that has a qualifying competent authority agreement with Belgium.

The return must include entity identification, ownership structure, the information needed to compute effective tax rates and top-up tax allocations, and a record of elections. The ordinary deadline is the last day of the fifteenth month after year-end, extended to the last day of the eighteenth month for fiscal years beginning no later than 31 December 2024. That implies, for example, that a calendar-year 2024 filing would ordinarily fall due on 30 June 2026.

Belgium has also made clear that these are not “light” returns. Article 48 treats the returns in sections II and III of Title 2, Chapter 11 as complexe aangifte, which brings ten-year investigation and assessment periods. Article 61 allows fines from EUR 2,500 to EUR 250,000 for incorrect, incomplete or late information and for failures relating to the declaration and payment of top-up tax. 

 The draft form for assessment year 2024 applies to fiscal years ending on 31 December 2023 or during 2024 before 31 December; the assessment year 2025 form applies to fiscal years ending on 31 December 2024 or during 2025 before 31 December.

Both use the same basic architecture: taxpayer identification, group identification, section 2.1 for IIR “in respect of itself”, section 2.2 for IIR in respect of jurisdictions or JV positions in which an ownership interest is held, section 3 for prepayments, and section 4 for final tax computation. The notes also state expressly that each taxpayer subject to Belgian IIR files its own return, so a single group may generate several Belgian IIR returns.

That last point matters in practice. The explanatory notes make the Belgian registration process central: the group name and the Belgian Pillar Two identification number (FIN) in the return must match the prior KBO registration, and the taxpayer’s Belgian KBO number must be used in the return. In merger, split and similar successor situations, the notes contemplate that an acquiring company may need to file twice: once as successor to the dissolved entity and once in its own name if it was itself already an IIR taxpayer during the year. The notes also clarify scope: Belgian IIR taxpayers are Belgian constituent entities that fall within article 31(1) and are not excluded by article 31(2) or (3); a Belgian permanent establishment cannot itself be an IIR taxpayer because it cannot be a parent entity.

A particularly welcome feature of the draft is its explicit alignment with the OECD GIR architecture. Belgium’s notes say that the return has been aligned, where possible, with the GIR and that field values are harmonised with GIR codes.

The OECD describes the GIR as a standardised information return intended to facilitate compliance with and administration of the GloBE Rules, and the January 2025 version includes a template that jurisdictions can use to notify that GIR information will be received through exchange of information. Belgian article 54 uses the same architecture by switching off local filing where a qualifying competent authority arrangement and foreign filing exist. In that sense, the Belgian consultation is really about how the domestic IIR return should interface with the wider GIR exchange system.

However, the Belgian return is not merely a local cover sheet for the GIR. It sits on top of Belgium’s own charging rules in articles 31 and 32, under which Belgian ultimate parent entities, qualifying intermediate parent entities and partially owned parent entities can be charged on their allocable share of top-up tax in respect of low-taxed constituent entities. Those Belgian provisions broadly track OECD Model Rules article 2.1 on the application of the IIR and article 5.2 on the determination of jurisdictional top-up tax. The form therefore has to do more than reproduce GIR data points; it has to translate them into a Belgian assessment position.

A key technical design choice in the draft is its subgroup logic.