The tariff you can plan for isn't the problem. It's the one that won't sit still.

This month the US tariff regime hits another turning point. For exporters, the lesson isn't about one rate or one deadline — it's about learning to trade when the rules keep moving.

In February, the US Supreme Court ruled that the emergency-powers basis the administration had used for its sweeping import tariffs was unlawful. Within hours, a replacement was in place: a temporary 10% surcharge on almost all imports, this time under Section 122 of the Trade Act of 1974, effective from 24 February. It is collected at the border on top of existing duties — so a product that used to carry a 4% rate now carries at least 14% — and trackers compiled from US federal notices put the average US tariff near 11%, its highest level since 1943.

The catch is that Section 122 is, by law, temporary. It expires on 24 July, and the President cannot extend it. But — and this is the part that trips exporters up — that does not mean tariffs simply fall away. The US Trade Representative has timed a set of Section 301 investigations to produce replacement tariffs on dozens of countries by that very date, and separate Section 232 measures on steel, aluminium, semiconductors and, from 31 July, pharmaceuticals, run on regardless. One door is scheduled to close on 24 July; others are being held open right behind it.

It is tempting to follow all this as a single figure — what's the rate today? — and to wait for it to settle before doing anything. That is the wrong instinct, because the defining feature of this moment is not the height of the tariff wall but its instability. In a matter of months the legal basis has been struck down at the Supreme Court, replaced, challenged, struck down again at a lower court, then reinstated on appeal while the case grinds on — possibly back to the Supreme Court. The rate could yet climb toward its 15% ceiling; it could splinter country by country; it could lapse and be patched over sector by sector. Nobody — not the importers paying it, not the lawyers advising them — can tell you with real confidence what the landed cost of a US-bound shipment will be six months from now.

That uncertainty is itself the cost. A predictable 10% tariff is just a line in a spreadsheet: you adjust your price, absorb a little, and carry on. A tariff that might be 10%, or 15%, or zero, or quietly replaced by something narrower and more durable, is something you cannot price, cannot quote a customer against, and cannot plan inventory around. Little wonder that in one survey of senior trade professionals this year, 72% named US tariff volatility as the single most impactful regulatory change they face — up from 41% the year before. The number that matters isn't the tariff. It's how many businesses now treat trade policy as a live planning variable rather than a fixed cost of doing business.

If you sell into the United States — or might — three consequences follow. First, your American buyer's appetite is now partly a function of their own tariff exposure. An importer staring at an uncertain landed cost is a cautious buyer: slower to commit, quicker to push that risk back up the chain to you in the form of price pressure or shorter commitments. Second, the temptation to reroute — shipping through a third country to soften the hit — is real but hazardous. Rules of origin are precisely what the new Section 301 measures are built to police, and a clumsy rerouting turns a tariff problem into a compliance one. Third, and most quietly, the squeeze falls hardest on the smallest exporters. A large firm has a trade team to model scenarios and a balance sheet to absorb a bad month; a small exporter has neither, and a single shipment mispriced into a 15% wall can swallow the margin on several good ones.

There is a wider point here too, and it outlasts this particular episode. Whatever happens on 24 July, the era of treating tariffs as a stable backdrop is over. Policy volatility is now a permanent feature of the landscape — not only in Washington — and the exporters who thrive will be the ones who plan for it rather than hope it away.