UK CBAM vs EU CBAM (2027): The Practical Differences for Importers

If you import into both the UK and the EU, or you are simply trying to work out whether "CBAM" means one thing or two, the short answer is two. The UK and the EU are each building a carbon border charge under the same name, but the mechanics, the numbers, and the filing calendars do not match. This guide lays out where they agree, where they diverge, and what that means for an importer sitting across both markets.

UK CBAM applies from 1 January 2027. EU CBAM is already live: its definitive period began on 1 January 2026, after three years of reporting-only obligations. So for the next while, the EU scheme already carries a financial cost and the UK scheme does not yet, which changes how urgently each side of your business needs to act.

The core difference: a tax versus a certificate market

The single biggest practical difference is how each government actually charges you. UK CBAM is a tax. HM Revenue & Customs (HMRC) sets sector-level rates and importers pay HMRC directly, on a return, like any other tax liability. There are no certificates to buy, hold, or surrender.

EU CBAM works differently. Importers must buy and surrender CBAM certificates, priced against the EU Emissions Trading System (ETS), in proportion to the embedded emissions of what they import. It is a market mechanism layered on top of the ETS carbon price, not a fixed tax rate, so the EU cost moves with the ETS price and the phase-in schedule.

In practice: a UK importer computes a tax bill from a published rate. An EU importer has to track a moving certificate price and manage a certificate position. The EU side is the more operationally involved of the two.

Default values: one number per good versus country-specific figures

Both schemes need a fallback emissions figure for when an importer cannot get verified, installation-level data from their supplier — that is what a "default value" is, on either side of the Channel. How each government builds that fallback is where they part ways.

HMRC will publish one default value per CBAM good, in advance, fixed for an initial period from 2027. There is no country breakdown: the same figure applies to a given good regardless of where it was made, and it does not carry a published escalating markup the way the EU figure does.

The EU publishes country-specific default values under Commission Implementing Regulation (EU) 2025/2621, so the same product can carry a different default depending on the exporting country. On top of that, the EU applies an escalating markup to push importers toward reporting actual data — reported at roughly 10% in 2026, rising toward 30% by 2028 for most goods (fertilisers rise more gently, about 1% a year). Full detail on that schedule is in CBAM default values explained.

The upshot: an EU default is a moving, country-aware number designed to get more expensive each year you keep using it. A UK default is a single fixed figure, at least for its initial period, with no country lookup and no announced yearly escalation.

Scope: the UK leaves out electricity

Both schemes cover the same core industrial ground — iron & steel, aluminium, cement, fertilisers, and hydrogen. The one scope difference that trips people up is electricity. EU CBAM covers electricity as one of its sectors. UK CBAM does not: electricity sits outside UK CBAM's scope entirely.

Glass and ceramics are worth a note too, since they appeared in the UK's original 2023 proposal. They were formally excluded from UK CBAM following the 2024 consultation, so if your business handles those goods, they are out of scope for the UK charge (they were never in scope for EU CBAM in the first place).

Registration thresholds: value-based versus mass-based

Both governments exempt small importers, but they measure "small" differently. UK CBAM uses a £50,000 rolling 12-month threshold, a value-based test on the price of the goods you bring in. EU CBAM instead uses a 50-tonne net-mass threshold per importer per year, a volume-based test that ignores price entirely.

Because the two tests measure different things, a business can be over one threshold and under the other. A high-value, low-weight import could clear the UK's £-based bar while staying under the EU's 50-tonne bar, and vice versa for something heavy but cheap. Check each threshold on its own terms rather than assuming clearing one tells you anything about the other. If you want to test your own numbers against the UK side, use the UK threshold checker.

First filing: different clocks, different amounts due

UK CBAM's first accounting period is calendar year 2027. Registration for that period stays open until 31 January 2028, and the first UK return and payment are due by 31 May 2028.

On the EU side, the definitive period began 1 January 2026, so EU importers are already accruing a liability. Certificate sales for 2026 emissions were postponed to 1 February 2027, and the first surrender against 2026 imports is due by 30 September 2027 — earlier in the calendar than the UK's first return, and against an obligation that started a year sooner.

Put simply: by the time a UK importer is filing their first return in mid-2028, an EU importer will already be well into their second annual cycle.

Side by side

What this means if you import into both markets

Treat UK CBAM and EU CBAM as two separate compliance tracks rather than one problem with two names. They will ask for different data at different times: the EU wants country-specific actuals to beat an escalating markup, right now; the UK wants you to know your rolling import value against a fixed threshold, from 2027. Confirm your position on each threshold separately, and build your supplier data collection so it can serve both trackers rather than duplicating the work per market.

This page compares the two regimes at a practical level. For the EU mechanics in full, see CBAM default values explained and how to calculate your CBAM costs. For the UK side, see the UK CBAM overview.

This guide is informational, not legal or tax advice. UK CBAM rules are still being finalised by HMRC; confirm current requirements before making compliance decisions.