The QDMTT Safe Harbour is the reason a lot of groups expect to file very little top-up tax detail for jurisdictions with a domestic minimum tax. If a jurisdiction's QDMTT meets the relevant standards, the top-up tax computed under the GloBE rules for that jurisdiction is treated as nil, and the QDMTT does the work locally. One of those standards is about which accounts the QDMTT is computed from. That is where differing year-ends have caused real uncertainty, and where the guidance published on 11 September 2026 lands.
The rule in one paragraph
A QDMTT can be computed from the local financial accounting standard rather than the standard used in the consolidated accounts. The question has been: what if the local accounts cover a different period? The guidance says the comparison that matters is between the entity's local accounting period and the period used for that entity in preparing the consolidated financial statements. That is not necessarily the ultimate parent's fiscal year. Where those two periods match, the difference in year-end with the parent does not by itself take the safe harbour away.
When a mismatch is still allowed
Where the local period and the consolidation period do differ, the guidance accepts it in two situations:
- Domestic law sets the period. A jurisdiction can prescribe a Required QDMTT Fiscal Period, and the local accounting standard can then be used if the other conditions are met.
- A restructuring caused it. The difference comes from an acquisition, disposal, merger or the establishment of a permanent establishment in the current or the immediately preceding fiscal period.
Outside those two cases, a mismatch is a problem worth raising before the filing season rather than during it.
Testing more than one period
This is the practical sting. Where a Required QDMTT Fiscal Period differs from the consolidation period, safe harbour eligibility has to be tested for every local period that begins and ends within the ultimate parent's fiscal year. If the safe harbour fails for any of them, that affects the outcome for the parent's year.
For a group whose spreadsheet assumes one QDMTT result per jurisdiction per year, that is a structural change rather than an extra column. Each local period needs its own data, its own computation and its own evidence.
Relief for the 2024 transition year
The guidance gives some room for the first year. For an ultimate parent fiscal year beginning on 31 December 2023 or during 2024, the safe harbour can be available if it applies to a Required QDMTT Fiscal Period that begins within that year, even where that only gives partial-year coverage. The relief does not apply where the Switch-off Rule applies to any of the relevant periods.
What to do now
- List every constituent entity whose statutory year-end differs from the period used for it in the consolidated accounts. Many groups don't keep that list in one place.
- Check each jurisdiction's QDMTT legislation for a Required QDMTT Fiscal Period.
- Flag restructurings (acquisitions, disposals, mergers and new permanent establishments) in the current and previous period, with dates.
- Where more than one local period falls inside the parent's year, build a separate test for each. Keep the source figures for each period, not just the result.
- Revisit 2024 positions that relied on the safe harbour across a mismatched period, in light of the transition relief and its Switch-off Rule carve-out.
Pillar2OS records the period each entity's figures come from, so a jurisdiction with two local QDMTT periods inside one group year shows two traceable tests rather than one blended number. See how the trace works.