OECD Pillar Two: The Global Minimum Tax Explained

OECD Pillar Two — often called the global minimum tax — is reshaping how the world's largest companies calculate and pay corporate tax. For finance professionals studying international tax as part of ACCA or CIMA, or working in a multinational group's tax function, Pillar Two is now one of the most practically important tax developments since transfer pricing rules became mainstream.

What is Pillar Two?

Pillar Two is part of the OECD/G20 Inclusive Framework's two-pillar solution to the tax challenges of a digitalised economy, alongside Pillar One (which reallocates taxing rights over the largest multinationals). Pillar Two introduces a global minimum effective tax rate of 15% for large multinational enterprise (MNE) groups, implemented through a set of coordinated rules known as the Global Anti-Base Erosion (GloBE) Model Rules.

Who does it apply to?

Pillar Two applies to MNE groups with consolidated annual revenue of at least €750 million in at least two of the four preceding fiscal years — the same revenue threshold used for country-by-country reporting. Groups below this threshold fall outside Pillar Two's scope, although many are still watching the rules closely as they may grow into scope or supply into groups that are affected.

The mechanics: IIR, UTPR and QDMTT

Pillar Two operates through three interlocking mechanisms designed so that, wherever a group is under-taxed, someone in the structure collects a top-up tax:

• Income Inclusion Rule (IIR) — the primary rule. It requires a parent entity to pay a top-up tax on the income of any group entity taxed below the 15% minimum rate, generally beginning for fiscal years starting on or after 31 December 2023.
• Undertaxed Profits Rule (UTPR) — a backstop that applies when the IIR does not fully capture the top-up tax, for example because the ultimate parent is in a jurisdiction that hasn't implemented Pillar Two. It generally applies for fiscal years starting on or after 31 December 2024.
• Qualified Domestic Minimum Top-up Tax (QDMTT) — a mechanism that lets the jurisdiction where the low-taxed profit arose collect the top-up tax itself, rather than ceding that revenue to another country's IIR.

Why it matters for finance teams

Pillar Two is not a simple tax-rate check. Groups must calculate an effective tax rate on a jurisdiction-by-jurisdiction basis using a specific GloBE income definition that starts from consolidated financial accounting figures and applies its own set of adjustments — meaning finance, tax and reporting teams all need to be involved. Compliance also brings a significant new reporting burden: the GloBE Information Return requires detailed jurisdictional data that most groups' existing systems were not originally built to produce.

Global adoption so far

Almost all members of the OECD/G20 Inclusive Framework on BEPS — over 140 jurisdictions — have agreed to the Pillar Two approach, and a large number, including all EU member states under the EU Minimum Tax Directive, the UK, and many other major economies, have already enacted domestic legislation implementing the IIR, UTPR and/or a QDMTT. The OECD estimates Pillar Two could generate around USD 150 billion in additional global tax revenue annually once fully implemented, largely by reducing the incentive for multinationals to book profits in very low-tax jurisdictions.

How Pillar Two relates to other OECD tax work

Pillar Two builds directly on the OECD's earlier Base Erosion and Profit Shifting (BEPS) project, which first targeted artificial profit shifting to low-tax locations, and it interacts closely with existing transfer pricing rules, since both frameworks depend on accurately allocating profit to the jurisdictions where real economic activity happens. A group with robust transfer pricing documentation is generally in a stronger position to produce the jurisdictional data Pillar Two compliance demands.

Common implementation challenges

In practice, groups working through Pillar Two compliance tend to hit the same few obstacles. Data availability is the biggest one: the GloBE calculations need granular, jurisdiction-level figures — current tax expense, deferred tax, substance-based income exclusions — that many ERP and consolidation systems were never configured to produce automatically. Safe harbours, including a transitional country-by-country reporting safe harbour, offer some relief by letting qualifying groups avoid the full GloBE calculation in lower-risk jurisdictions, but only for a limited period. Groups also have to navigate different implementation timelines and technical choices across the jurisdictions they operate in, since not every country has adopted the IIR, UTPR and QDMTT in the same combination or on the same schedule, which means a genuinely global compliance approach has to be built jurisdiction by jurisdiction rather than applied as a single uniform template.

FAQs

Does Pillar Two replace transfer pricing rules? No. Transfer pricing determines how profit is allocated between related entities; Pillar Two then applies a minimum tax test on top of that allocation.

What happens if my group's effective rate is below 15% in a country? A top-up tax is triggered, collected via the QDMTT if that country has one, or otherwise via the IIR at the parent level, or the UTPR as a final backstop.

Is Pillar Two only relevant to large listed multinationals? Its direct scope is the €750 million threshold, but subsidiaries, joint ventures and even suppliers of in-scope groups are increasingly asked to provide Pillar Two-relevant data, so its practical reach is wider than the headline threshold suggests.

Pillar Two represents a fundamental change in how multinational groups plan and report tax, and it is quickly becoming core knowledge for any finance professional working in international tax, group reporting, or tax advisory roles.