Corporate taxation is entering a new era. For decades, global companies could lower their tax bills by shifting profits across borders, leveraging incentives and complex international structures. The global minimum tax (GMT) changes that equation. Now, the world’s largest multinationals face a baseline tax rate no matter where they operate – a shift that is already reshaping strategies, reporting systems, investment patterns and the politics of global finance.
The GMT was designed inside the Organisation for Economic Co-operation and Development (OECD) over many years to ensure that large multinational enterprises (MNEs) pay at least a 15% effective tax rate wherever they operate. For years, governments have competed to attract investment by lowering corporate tax rates or offering incentives. The GMT is an effort to set a floor beneath that competition. The rules allow governments to collect “top-up” taxes if a company’s effective rate in a particular jurisdiction falls below 15%. They do this through three core tools: the “income inclusion rule,” the “undertaxed profits rule” and the “qualified domestic minimum top-up tax.”
It is “the first time we’ve seen a globally coordinated tax system of this scale,” says Cory Perry, a partner in Grant Thornton’s Washington National Tax Office. More than 50 countries have adopted similar rules, marking a shift from the long-standing model in which each country independently designed its corporate tax regime. The GMT is not just a technical adjustment to international tax rules; it marks a shift in how nations compete, how corporations plan and how value is measured across borders.
Canada has already moved from discussion to implementation. The Global Minimum Tax Act (GMTA), enacted in late 2024, applies to MNEs with at least €750 million in global consolidated revenue in two of the previous four fiscal years. For these organizations, the question is no longer whether the rules matter; it’s how they will adapt their reporting and internal systems to comply. The Canada Revenue Agency opened registration for the GMTA in October 2025, but the official “GloBE Information Return” form is still pending. The first reporting deadline is June 30, 2026.
Harry Chana, a cross-border tax services leader at BDO Canada, points to “confusion when it comes to regulations within the act that are relatively ambiguous” and which are generating unexpected impacts. For example, once a parent company’s global revenue passes the MNE threshold, the Canadian entity is automatically brought within scope.
Another misconception Chana highlights is the assumption that Canada’s relatively high corporate tax rates will shield companies from the new rules. “When you work through the actual rules and the complexities around how to calculate the 15%, in many cases it could apply to Canadian companies,” he says. Incentives and credits can lower a company’s effective rate below the threshold, making it subject to top-up calculations. For many businesses, this change will mean retooling accounting systems, building new data pipelines and preparing for higher administrative and compliance costs.
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The global picture
Wesley Boldewijn, a shareholder at Greenberg Traurig in Amsterdam who advises multinational clients across Europe, describes GMT implementation as uneven and complicated. “Every country is implementing the OECD framework in its own way, creating a patchwork of interpretations,” he says. “This means large companies may now face a more complex compliance environment that may result in higher taxes, double taxation and the challenge of applying multiple reporting standards within one organization. Some multinationals may end up paying more in fees to advisory firms to implement and monitor these new tax rules than they currently pay in top-up tax.”
Some companies are responding by restructuring their subsidiaries to consolidate taxable profit in jurisdictions where calculations are predictable. Others are weighing the value of tax incentives that could, under the GMT, have the opposite of their intended effect. The incentive landscape is already shifting: countries are moving away from direct tax breaks and toward refundable credits that preserve competitiveness while staying within the GMT’s guardrails.
According to Abdul Muheet Chowdhary of the South Centre, in the United Kingdom, “the GMT has virtually no benefits” for developing countries and may even increase reliance on subsidies in place of traditional tax incentives. Tommaso Faccio, head of the Secretariat of the Independent Commission for the Reform of International Corporate Taxation, sees the core issue as the rate itself. He argues that the floor should be 25% instead. Still, some lower- and middle-income countries have begun adopting the minimum, particularly where tax incentives have historically drained public revenue.
The politics behind the GMT
Recent G7 discussions signalled that U.S. companies may be treated differently under a “side-by-side” framework that acknowledges the United States’ own minimum tax regime. That raised questions abroad about whether the GMT still ensures a level playing field. The European Union has moved forward with broad implementation, while U.S. policymakers have voiced concerns, proposed carve-outs and in some cases sought to undermine adoption entirely.
Perry, with Grant Thornton, stresses that for many companies, the real challenge isn’t the tax itself. “What we’re seeing for many companies is that the impact is less about an increased tax burden and more about an increased compliance burden,” he says. Even companies that do not owe significant top-up taxes must reengineer parts of their planning systems, gather new data inputs and prepare to file returns in multiple jurisdictions. “In practice, it is often more of a resource strain than a cash tax strain,” Perry notes.
Certain sectors feel the effects more acutely. Infrastructure companies, for example – those operating in energy, transportation, utilities or water – rely on long-term investments, regulated returns and complex financing arrangements. These features interact with the GMT’s country-by-country effective tax rate calculations in ways that can produce unexpected results. Some organizations are already preparing for increased deferred tax adjustments and expanded disclosure requirements in financial statements.
The takeaway for multinational businesses is straightforward: start now. Map global structures, evaluate jurisdictional effective tax rates, test financing and revenue models, and plan for increased interaction with regulators and investors. The rules are still evolving, and transitional uncertainty will likely last years. But waiting will only make compliance harder.
Gordon Feller is a writer based in San Francisco.
