Changing the Payoff, Not the Price

Everything so far has described a system trying, and largely failing, to make profit appear where activity happens. The arm's-length principle could not price unique intangibles. Substance rules raised the cost of shifting without removing the incentive. The pattern of the 2010s was a treasury patching seams faster than firms could find new ones, and losing on points. The global minimum tax — the second of two pillars in the OECD-coordinated reform agreed in outline by well over a hundred jurisdictions around 2021 — is an attempt to stop playing that game and change the scoreboard instead.

The core idea is a floor. Large multinational groups — the reform targets the biggest, those above a high revenue threshold, not the corner shop — should pay at least a minimum effective rate on their profit in every country where they book it. That floor was set at 15%. Note the two adjectives doing quiet work. "Minimum": countries remain free to tax above it, and many do; the reform sets a floor, not a ceiling or a common rate. "Effective": what matters is the actual tax paid on the profit after all the deductions and credits, divided by the profit — not the headline statutory rate a country advertises. A country can post a respectable statutory rate and, through generous carve-outs, deliver a low effective rate. The minimum tax looks through the advertisement to the reality.

Now the mechanism that gives the floor its bite. Suppose a group books profit in a country where its effective rate comes to 5%. That is 10 percentage points below the floor. The system permits another country — under the primary rule, the country where the ultimate parent resides — to levy a top-up tax collecting roughly that 10-point shortfall. The profit that escaped tax in the low-rate jurisdiction gets caught elsewhere, brought up toward the 15% floor. There is a backstop, too: if the parent's country declines to apply the top-up, other countries where the group operates may claim it instead, through a secondary rule that allocates the uncollected top-up among them. The design intent is that the shortfall gets collected somewhere. There is nowhere for the profit to be that is fully out of reach.

Sit with what this does to incentives, because it is the whole point. Under the old system, moving profit into a 5% jurisdiction saved real money — that profit genuinely bore only 5%. Under the minimum tax, moving profit into that same jurisdiction is worth far less, because the 10-point gap gets topped up somewhere anyway. The group pays close to 15% on that profit whatever it does. The low-tax box has not been abolished; it has been devalued. And crucially, this was achieved without forcing the low-tax jurisdiction to raise its own rate. The reform did not need every country's agreement to lift rates — a thing no international body can compel. It only needed enough large economies to agree to collect top-ups. The floor is enforced by the countries that want it, reaching profit that others declined to tax.

There is a second-order twist worth understanding, because it changes who benefits. Faced with the certainty that the shortfall will be collected somewhere, a low-tax jurisdiction has a sharp new incentive: collect it yourself. If profit booked in your country will be topped up to 15% by somebody regardless, you may as well be the one to charge the extra tax — better in your treasury than a foreign one. So the reform includes a provision letting a jurisdiction impose its own domestic top-up, bringing its effective rate on in-scope groups up to the floor and keeping the revenue at home. The likely result is that some traditional low-tax jurisdictions simply raise their effective rate to 15% for large multinationals and pocket the difference themselves. The race toward zero has a floor now, and the floor is, in part, self-enforcing: the low-tax jurisdictions are nudged to collect the minimum rather than watch others collect it on their behalf.

A measured caveat, because enthusiasm here should be rationed. The floor is 15%, which is low — below the statutory rate of most large economies. It sets a modest minimum, not a levelling. The rules are enormously complex, with carve-outs, including one that reduces the top-up in proportion to real payroll and tangible assets a group has in a country — a deliberate concession that partly exempts profit backed by genuine substance. And the whole edifice depends on enough major jurisdictions actually enacting and enforcing it; a floor that only some countries hold up is a floor with gaps. What the minimum tax reliably does is compress the extremes — it makes the very lowest effective rates much harder to enjoy on paper profit. What it does not do is end tax competition, harmonise rates, or make the two maps converge. It narrows the range in which the game is played. That is a real achievement and a bounded one, and the next lesson traces what it does to the geography we actually care about.