For decades, multinational companies could reduce their tax bills by booking profits in jurisdictions with low rates, regardless of where the activity took place. A global minimum tax is designed to blunt that strategy by setting a floor on the rate companies pay on their worldwide income. The rules are complex, and their effect is beginning to show.
The reform is one of the most significant changes to international taxation in a century, and its implementation is uneven. Understanding what it does, and what it does not, is the key to reading the debate around it.
What the minimum tax does
The mechanism sets a minimum effective rate on the profits of large multinational groups. Where a company’s profits in a jurisdiction are taxed below that floor, another country may collect a top-up. The effect is to make shifting profits to a tax haven less rewarding, because the difference is clawed back somewhere in the group.
Why it took so long
Tax sovereignty is closely guarded, and a global rule requires coordination among many countries with different interests. Small jurisdictions that rely on low rates resisted, while larger economies sought to protect their revenue. The agreement that emerged is a compromise, and its adoption has been gradual.
Estimates of the revenue raised vary widely, and the amounts are modest relative to total corporate tax collections. The more important effect may be behavioural: companies have less incentive to structure operations purely for tax reasons. Whether that shows up in investment decisions is something researchers will track over years.
What companies are doing
Multinationals have been restructuring, reviewing their legal entities and reassessing where they book profits. Compliance costs have risen, particularly for groups that must calculate effective rates across many jurisdictions. Smaller firms are largely unaffected, because the rules apply above a size threshold.
Countries can still compete on tax, and some have adjusted other parts of their systems in response. The minimum tax narrows one form of competition without eliminating it. That is an important limit, and it explains why the reform is described as a floor rather than a harmonisation.
Implementation gaps
Adoption has been uneven, and some countries have delayed or adapted the rules. Where implementation is incomplete, companies face a patchwork, which raises compliance costs and creates opportunities for planning. The effectiveness of the reform depends on how widely and consistently it is applied.
The indicators worth following are corporate effective tax rates, the location of reported profits and the revenue collected by participating countries. Those will show whether the floor changes behaviour in practice, which is the test that matters more than the text of the agreement.
The role of developing countries
The reform has a particular significance for countries that lose revenue when profits are booked elsewhere. A minimum tax can return some of that revenue, and it also changes the incentives for companies operating in those markets. How the rules are implemented locally, and how much administrative capacity exists, determines whether the benefit is realised.
Implementation will continue to spread unevenly, and disputes about interpretation are likely. The framework may be adjusted as experience accumulates. The useful question is not whether the reform is perfect but whether it changes the behaviour it was designed to address, and that will take several years of data to answer.
The administrative burden
Applying the rules requires detailed data on profits, taxes and activities in each jurisdiction. Large groups have the systems and advisers to manage this; smaller ones find it harder. The reform therefore adds a fixed cost that is proportionally heavier for mid-sized companies, an effect its designers acknowledged and tried to limit with thresholds.
The measure of success is not the agreement’s text but the change in reported profits and effective rates over time. If profits stop migrating to low-tax jurisdictions, the reform is working. If they continue, the rules will be revised. That is the test, and it will take years of data to apply.
The political durability
Tax reforms can be reversed, and a change of government can alter implementation. The minimum tax is embedded in domestic law and international agreement, which makes reversal harder but not impossible. Its durability will depend on whether it is seen to raise revenue and whether the countries that benefit defend it. That is a political question as much as an economic one.
Why the numbers are contested
Estimates of the revenue the minimum tax will raise differ widely, because they depend on assumptions about how companies respond and how countries implement the rules. Supporters emphasise the revenue and the reduction in profit shifting; critics emphasise compliance costs and the possibility that investment moves elsewhere. The disagreement is not about arithmetic but about behaviour, and behaviour is what the coming years of data will reveal. Until then, both sides are reasoning from models rather than outcomes.
This report draws on the OECD’s work on international tax reform.
Image: U.S. Government Accountability Office from Washington, DC, United States · Public domain · via Wikimedia Commons.