On 6 January 2026, the Luxembourg tax authorities (LTA) have opened the registration module for in-scope Luxembourg entities and published the procedures for the Pillar II information return and top-up tax returns.
For background, Pillar II rules determine minimum taxation standards for international and domestic groups subject to meeting certain conditions.
Registration for Luxembourg entities under Pillar II is open
The Luxembourg law of 22 December 2023 on effective minimum taxation, as amended (Pillar II Law) requires each Luxembourg constituent entity in an in-scope multinational enterprise (MNE) group or large-scale domestic group (Domestic Group) to register with the LTA.
Who must register?
Every Luxembourg constituent entity of an in-scope MNE or Domestic Group must register with the LTA within the statutory timeline. This obligation also applies where a Luxembourg entity becomes part of such a group during the year in question. Joint ventures and entities affiliated to a joint venture that are located in Luxembourg are subject to the same registration, change-notification and deregistration obligations.
Information to provide on registration
The Pillar II Law specifies the minimum data that must be provided to the LTA when registering:
- Identity of the Luxembourg constituent entity and its national identification number;
- Group name (MNE or Domestic Group);
- Identity and jurisdiction of the ultimate parent entity (UPE);
- The first fiscal year in which the group falls within scope of the Pillar II Law and the group’s fiscal year‑end date;
- Identity of the designated local filing entity (if any);
- Identity of the designated “top entity” for the undertaxed profits rule (UTPR) and for the Luxembourg qualified domestic minimum top‑up tax (QDMTT) where applicable;
Luxembourg entities must also notify the LTA of any subsequent change to the registered information within 15 months after the last day of the reportable fiscal year in which the change occurred, and must deregister within 15 months after the last day of the reportable fiscal year in which the group falls out of scope or the entity ceases to be a Luxembourg constituent entity.
Deadlines
- Registration: within 15 months of the end of the reportable fiscal year in which the group becomes in scope, extended to 18 months for the transition year.
- Transitional rule: The Pillar II Law provides that notwithstanding the above, the first registration for Luxembourg constituent entities part of an in-scope group should occur no later than 30 June 2026.
Penalties for registration and notification failures
Failure to register on time, notify changes on time, or provide incomplete/incorrect information may trigger a fixed fine of EUR 5,000 per Luxembourg constituent entity.
Other filing obligations
The LTA has released the procedures for:
- The Pillar II top‑up tax information return (for Income inclusion rule (IIR)/UTPR and Luxembourg QDMTT) and;
- The top‑up tax returns for IIR, UTPR and Luxembourg QDMTT.
Information return: deadline and penalties
- The Pillar II information return must be filed no later than 15 months after the last day of the reportable fiscal year (18 months for the transition year under the general transitional rule). This means that the deadline for filing the information return is 30 June 2026.
- Failure to file the information return on time (or filing an incomplete/inaccurate return) may be sanctioned with a fine of up to EUR 250,000.
If a foreign filing is not obtained via automatic exchange after notification, a fine of up to EUR 300,000 may apply following an LTA request; this is separate from the EUR 250,000 cap for domestic filing failures. This higher penalty applies where (i) a Luxembourg entity (or the designated local entity) has relied on a foreign filing of the Pillar II information return (by the UPE or a designated surrogate in another jurisdiction with an eligible competent authority agreement), (ii) has duly notified the LTA of that foreign filer and jurisdiction, but (iii) there is no effective automatic exchange of information on such return (subject to remedial mechanisms).
Top‑up tax returns: deadlines, assessment and payment
- The IIR, UTPR and Luxembourg QDMTT returns must be filed no later than 15 months after the last day of the reportable fiscal year, and the tax must be paid no later than one month after filing. This means that the deadline for filing the information return is 30 June 2026 and that the payment must occur at the latest on 31 July 2026.
- In case of non-filing or incomplete/inaccurate filing, the tax office will assess the underpayment by way of a tax bulletin. The assessed amount must be paid within one month from the issuance date of the tax assessment and late‑payment interest may also apply.
Group liability in Luxembourg
Each Luxembourg constituent entity is jointly and severally liable for the amounts due under the IIR, the UTPR and the QDMTT.
Our tax team is available should you have any questions regarding your Pillar II compliance obligations.
