On Thursday 19 March 2026, the Belgian tax authorities published the draft Income Inclusion Rule (“IIR”) top-up tax return and accompanying explanatory notice for assessment year 2024 (covering fiscal years starting at the earliest on 31 December 2023 and closed at the latest on 30 December 2024) and 2025 (covering fiscal years starting at the earliest on 31 December 2024 and closed at the latest on 30 December 2025). This publication forms part of a public consultation process, with large (domestic/MNE) groups invited to submit feedback by 3 April 2026.
What is the IIR Top-up tax return?
The IIR Top-up tax return should be filed on an annual basis within 18 months after the last day of the first reporting year in scope (15 months afterwards). For in-scope groups with a financial year aligned with the calendar year, this means the first due date to file the IIR top-up tax return will be 30 June 2026.
The draft IIR Top-up Tax Return is structured around the following key sections:
- Identification – identification of the taxpayer liable for IIR top-up tax in Belgium and the MNE group or large-scale domestic group as well as information on the Consolidated Financial Statements.
- IIR top-up tax – limited number of data points per Belgian subgroup including the option to opt for some elections and report the amount of top-up tax due under IIR with respect to the filing entity itself and to low-taxed constituent entities in which the Belgian parent entity holds participation.
- Prepayments – information regarding the prepayments made with respect to IIR. Please also refer to our newsflash in this respect.
- Final calculation of the IIR top-up tax due – per Belgian subgroup, the return includes a calculation sheet that determines the final IIR top-up tax due, taking into account the prepayments made (if any).
- Contact person – The return requires the designation of a contact person, including name, function, address, telephone number, and email.
Importantly, the return has been aligned with the Globe Information Return (“GIR”) to the extent possible. In practice, this means that the information required for the Belgian IIR top-up tax return largely mirrors what is already being compiled for GIR and QDMTT return purposes, such as group identification, constituent entity details, sub-group classifications, safe harbour elections, and top-up tax calculations.
Who must file the IIR top-up tax return?
It is our understanding that a filing obligation arises for a Belgian parent entity subject to IIR.
In addition, each taxpayer liable for IIR top-up tax must file its own return, meaning there may be multiple IIR returns for a single large (domestic/MNE) group. For the sake of completeness, a Belgian permanent establishment can never be a taxpayer for IIR purposes, as it cannot qualify as a parent entity.
Next Steps
To ensure the new return is as clear and efficient as possible, the Belgian tax authorities are seeking valuable feedback. Any feedback can be emailed to pillar2@minfin.fed.be in a Word document by 3 April 2026.
For the sake of clarification, the IIR top-up tax return is another compliance formality required in Belgium, apart from the GIR (Notification) for which we still expect the publication of the Belgian form.
How can we assist you?
We are happy to assist you with:
- Providing any assistance on Pillar 2, including data collection and computations of the top-up tax due under IIR; and/or
- Any assistance with preparing the IIR top-up tax return once the Belgian tax authorities published the final version.
Reach out to your regular contact person or Evi Geerts (e.geerts@pwc.com), Pieter Deré (pieter.dere@pwc.com), or Koen De Grave (koen.de.grave@pwc.com).
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