Twenty-five days. That’s how long you have before the UK’s first-ever Pillar Two global minimum tax filing deadline closes on 30 June 2026. If your group is in scope and you haven’t already started, you’re behind. This post is your CFO checklist — what needs to be filed, who it applies to, the three-scenario framework that determines your specific obligations, and what happens if you miss it.
What Pillar Two Actually Is — The 30-Second Version
Pillar Two is the OECD’s Base Erosion and Profit Shifting (BEPS) 2.0 framework for a global minimum effective tax rate of 15%. Large multinational groups must pay at least 15% tax in every jurisdiction where they operate. Where they don’t — because of low local tax rates, incentives, or structuring — a top-up tax is charged either in the parent jurisdiction (Multinational Top-up Tax, MTT) or, in the UK’s case, through a domestic top-up charge (Domestic Top-up Tax, DTT) that prevents the top-up going abroad. The UK implemented both charges through the Finance (No. 2) Act 2023, effective for accounting periods beginning on or after 31 December 2023. Now the first filing cycle has closed and returns are due.
Who Is In Scope: The Two-Part Test
You’re in scope for the June 30 deadline if your group satisfies both of the following:
- Revenue threshold: The MNE group has recorded consolidated annual revenues of €750 million or more in at least two of the last four accounting periods.
- UK nexus: The group has at least one UK taxable entity (subsidiary, branch, or permanent establishment).
The rules apply to accounting periods beginning on or after 31 December 2023. For December year-end groups, this means the first period in scope is the year ending 31 December 2024, and the 18-month extended filing window closes — irreversibly — on 30 June 2026. After this transitional extension, subsequent returns will be due within 15 months of the period end, so December 2025 year-ends will be due 31 March 2027.
Smaller groups — below the €750m threshold — are outside scope, but be aware of the joint venture aggregation rules and deemed consolidation provisions that can pull in groups that appear to sit below the line. If your external auditors flagged Pillar Two disclosures in your December 2024 accounts, you are almost certainly in scope.
The Three Compliance Scenarios
Your specific filing obligations depend on where your ultimate parent entity (UPE) is located and whether that jurisdiction has implemented Pillar Two. Azets and Buzzacott have published useful frameworks, which I’ll summarise here.
Scenario 1 — Parent jurisdiction has fully implemented Pillar Two. This is the cleanest scenario. UK entities must submit an Overseas Return Notification (ORN) to HMRC identifying the jurisdiction where the GloBE Information Return (GIR) is being filed centrally. They must also file a UK Pillar Two self-assessment return via HMRC-approved specialist software. If the UK entity holds any low-tax subsidiary within the group structure, it may owe actual top-up tax — requiring payment on or before 30 June 2026. UK parent companies of large groups must additionally file the GIR itself.
Scenario 2 — Parent jurisdiction has not and will not implement Pillar Two (most commonly: US-parented groups). The US operates its own parallel regimes — GILTI (Global Intangible Low-Taxed Income) and CAMT (Corporate Alternative Minimum Tax) — but these are not equivalent to OECD Pillar Two for filing purposes. US-parented UK groups cannot simply defer to parent-level compliance. They remain required to submit a UK Pillar Two return and may carry top-up tax liability in the UK. The OECD announced a new Side-by-Side (SbS) exemption that provides transitional relief for US-parented groups, but this applies only to periods beginning on or after 1 January 2026 — it does not help with December 2024 period filings due on 30 June. This is the scenario with the highest risk of underestimating UK obligations.
Scenario 3 — Parent jurisdiction is implementing but not yet effective for December 2024 year-ends. Some jurisdictions are mid-implementation. Here, UK entities face filing obligations including the ORN, and may carry top-up liability in the UK depending on the group’s effective tax rates jurisdiction-by-jurisdiction. Early assessment is critical because the filing requirement doesn’t wait for the parent jurisdiction to catch up.
What You’re Actually Filing — The Three Documents
There are potentially three separate documents in play for a UK entity:
- UK Pillar Two self-assessment return: Mandatory for all in-scope UK entities, even where no top-up tax is due. Filed via HMRC-approved software (not the standard Corporation Tax return). Details any DTT and MTT liability. HMRC’s guidance on paying Pillar Two top-up taxes confirms payment must be made using a specific Pillar Two ID reference via bank transfer.
- GloBE Information Return (GIR): The master information return containing entity-level and jurisdiction-level data across the entire group. Can be filed centrally in one jurisdiction if that jurisdiction has an information-sharing agreement with HMRC. If filing centrally elsewhere, the UK entity files the ORN instead. KPMG notes that the OECD has recently clarified the central filing framework following updated administrative guidance.
- Overseas Return Notification (ORN): A notification to HMRC identifying where the GIR is being filed, when it’s being filed abroad. Simpler than the GIR itself but still a formal HMRC submission.
Safe Harbours — Are You Eligible?
Before calculating a top-up tax liability from scratch, check whether your group qualifies for one of the transitional safe harbour elections. The Transitional Country-by-Country Report Safe Harbour (TCSH) — also called the Qualified Domestic Minimum Top-up Tax (QDMTT) safe harbour — uses Country-by-Country Report (CbCR) data to provide a simplified test. If the jurisdiction’s revenues are below de minimis thresholds, the effective tax rate passes the simplified ETR test, or the substance-based income exclusion exceeds the residual profit, the top-up tax for that jurisdiction is deemed nil. These elections must be made on the return itself and can substantially reduce compliance burden. BDO’s guidance on safe harbour elections is worth reviewing if your team hasn’t already modelled eligibility.
Note: safe harbour eligibility requires your CbCR data to be reliable and consistent with your Pillar Two calculations. Groups that have previously used local-GAAP simplifications in CbCR data should verify that the data is fit for purpose before relying on safe harbour elections.
Data: The Operational Problem Nobody Solved Early Enough
Pillar Two is not an accounting exercise. It’s a data infrastructure problem. The GloBE calculations require granular, entity-level data across every jurisdiction — covered taxes, deferred tax positions, substance-based income exclusions (payroll and tangible asset carve-outs), cross-jurisdictional allocations, and adjustments for M&A transactions mid-period. Most ERP systems were not built to produce this data in the required format. Finance teams that assumed their CbCR process would carry over intact to Pillar Two have largely been disappointed.
If your group is in scope and doesn’t yet have a compliant data pipeline: get external support immediately. RSM’s Pillar Two readiness framework identifies seven data categories that cause most calculation errors. With 25 days remaining, you’re in a race against HMRC’s clock.
Registration: Should Have Happened by June 30, 2025
HMRC required in-scope groups to register within six months of the end of their first in-scope accounting period. For December 2024 year-ends, that registration deadline was 30 June 2025 — a year ago. If your group didn’t register then, you’re late. HMRC is not yet in aggressive enforcement mode on registration failures, but late registration ahead of the filing deadline is a material risk you should document and self-disclose. PKF Francis Clark sets out the registration mechanics if your group still needs to complete this step.
Penalties for Missing the Deadline
The UK Pillar Two penalty regime mirrors the corporation tax framework. Failure to file the self-assessment return on time triggers automatic fixed penalties. Interest runs on unpaid top-up tax from the payment due date. HMRC can also investigate the underlying GloBE calculations and raise discovery assessments where the return is found to be incorrect. Given that the June 30, 2026 deadline is the first and HMRC has signalled it is actively monitoring compliance, the risk of a light-touch initial response should not be assumed. AccountingWeb’s Pillar Two FAQ covers the penalty structure in accessible detail.
CFO Action Points — June 2026
- Confirm scope immediately. Check revenue threshold across last four periods and identify all UK entities. If in doubt, assume in scope and work backwards.
- Verify registration status. Confirm your group registered with HMRC by June 30, 2025. If not, register now and document the delay.
- Identify your filing scenario. Determine parent jurisdiction’s Pillar Two implementation status. US-parented groups should not assume SbS exemption applies to this deadline.
- Assess safe harbour eligibility. Run the TCSH test against your CbCR data before calculating full GloBE liability. Document the basis for any elections.
- Lock down your data pipeline. Reconcile GloBE data to management accounts and tax provisions. Identify gaps in deferred tax and substance-based exclusion data.
- Book approved software. The UK Pillar Two return cannot be filed via HMRC’s standard CT600 gateway. You need specialist software — most advisers are already at capacity with June clients.
- Arrange payment mechanics. Obtain your Pillar Two ID from HMRC and test the payment channel before deadline day. Bank transfer is required; don’t leave this to the last 24 hours.
- Brief the board. Pillar Two top-up tax is a P&L charge. Where material, it requires disclosure in statutory accounts and should feature in tax strategy documentation.
The Bigger Picture
Pillar Two is permanent. The June 30 deadline isn’t a one-off event — it’s the start of an annual compliance cycle that will sit alongside, and interact with, your existing corporation tax obligations indefinitely. Groups that build proper infrastructure now — clean data, documented safe harbour positions, tested filing software — will have a significant operational advantage over those that treat each deadline as a crisis to be managed. The next deadline (for December 2025 year-ends) comes around on 31 March 2027, and the regime will be maturing: HMRC scrutiny will intensify, safe harbour transitional provisions will begin to narrow, and the OECD is already consulting on further administrative guidance changes.
If your group is in scope and you haven’t started, start today. If you’ve started but haven’t stress-tested the data, stress-test it now. If you’re confident the return is ready, run the payment test. Twenty-five days is enough time — but only if you use them.
Need help with Pillar Two compliance, GloBE calculations, or UK filing obligations? Contact Mark Hendy at Tanous — a PE-facing CFO with deep international tax and compliance experience. Whether you need a second opinion on your safe harbour position or hands-on support with the June 30 return, get in touch.