UK CBAM registration is triggered when a business crosses £50,000 of CBAM goods, tested two separate ways: a backward-looking 12-month calculation and a forward-looking 30-day forecast. HMRC's Policy Summary, updated 9 April 2026, confirms that businesses normally have 30 days to register once either test is met, but the deadline is extended in the mechanism's first year. Registration itself will run through HMRC's Government Gateway, and as of July 2026 that portal is expected to open in the final quarter of 2026, later than the Q3 2026 window some earlier coverage suggested. This page walks through both threshold tests, the registration deadline rules, the Government Gateway timeline, and the first return periods that follow registration.
What Is the UK CBAM Registration Threshold?
The UK CBAM registration threshold is £50,000 of CBAM goods, and a business must register with HMRC once it meets or exceeds that value under either of two separate tests. This is a value-based threshold, not the mass-based test used under EU CBAM, which exempts importers below 50 tonnes of covered goods per year regardless of value. UK CBAM measures pounds sterling of covered imports, not tonnes, so a business importing a small volume of high-value goods can cross the UK threshold well before comparable EU exposure, and vice versa for bulk, low-value goods.
CBAM goods for this purpose are imports falling within the sectors set out in UK CBAM legislation: aluminium, cement, fertilizers, hydrogen, and iron and steel. The UK CBAM guide covers the full sector and product scope; this page focuses only on the registration mechanics that follow once a business is importing those goods.
The Two £50,000 Threshold Tests, Explained
HMRC applies two independent tests to the £50,000 threshold, and a business only needs to meet one of them to trigger a registration obligation. The two tests are described below.
- The backward-looking test. On the first day of each month, a business looks back over the preceding 12-month period and checks whether the total value of CBAM goods that have passed the tax point during that period met or exceeded £50,000. This test catches businesses that have built up steady import volume over time, even without any single large shipment.
- The forward-looking test. On any given day, a business must assess whether it expects the total value of CBAM goods it will import over the next 30 days to meet or exceed £50,000. This test catches businesses about to take on a large shipment or a new supply contract that will push them over the threshold immediately, before 12 months of import history exists.
Running both tests matters because they catch different risk profiles: a new importer with no import history could fail the backward-looking test every month yet still trigger the forward-looking test the day a large order is confirmed. Businesses close to £50,000 in either direction should check both tests on a recurring schedule, not just once at the start of the year.
The table below summarizes the two tests side by side.
| Test | Measurement window | What it checks | Who it typically catches |
|---|---|---|---|
| Backward-looking | Preceding 12 months, checked monthly | Actual value of CBAM goods already imported | Steady, established importers building up volume over time |
| Forward-looking | Next 30 days, checked on any given day | Expected value of CBAM goods about to be imported | New importers or those about to take on a large order or contract |
How Many Days Do You Have to Register With HMRC?
Businesses normally have 30 days to register with HMRC once they meet either threshold test, but the mechanism's first year carries an extended deadline. Any business that first becomes liable to register during 2027 has until 31 January 2028 to complete registration, rather than the standard 30-day window.
Two points follow from this rule.
- The extension applies to the year of first liability, not to every business indefinitely. A business that becomes liable in 2027 gets until 31 January 2028; a business that first crosses the threshold in 2028 or later must register within the standard 30 days.
- Missing either deadline exposes unregistered imports to liability regardless of registration status. Registering late does not remove the CBAM charge on covered goods imported while unregistered, and HMRC applies its standard tax-administration penalty powers to registration failures, covered in more detail in the UK CBAM compliance guide.
Businesses expecting to cross the threshold for the first time in 2027 should still register as soon as the test is met rather than wait for the extended deadline, since 31 January 2028 is a backstop, not a target.
When Does HMRC Registration Open?
Registration for UK CBAM will run through HMRC's Government Gateway, the same online portal HMRC uses for other tax registrations, and as of July 2026 that registration function is expected to open in the final quarter of 2026 (Q4 2026), a later window than the Q3 2026 date suggested by some earlier coverage. The shift followed the close of HMRC's second technical consultation on 21 May 2026; law firm and advisory coverage of HMRC's subsequent statements points to Q4 2026 as the current expectation, though HMRC has not published a specific opening date.
The registration timeline sits downstream of the underlying secondary legislation. HMRC ran two rounds of technical consultation on the draft rules that determine how registration, emissions calculation, and verification will work in practice.
- First technical consultation (registration and tax administration): ran 10 February to 24 March 2026
- Second technical consultation (emissions and verification): ran 9 April to 21 May 2026, covering embedded-emissions calculation, monitoring and verification procedures, and per-sector system boundaries for aluminium, cement, fertilizers, hydrogen, and iron and steel
With both consultations closed, the government's stated position as of July 2026 is that it is reviewing all responses and expects to lay the full set of final statutory instruments in autumn 2026, ahead of the Government Gateway registration window opening later in the year. Until those instruments are finalized and HMRC confirms an exact opening date, businesses should prepare their registration data now and treat any specific Q4 2026 date as provisional.
What Happens After You Register: First Accounting Period and Deadlines
Registration is the entry point into UK CBAM, not the end of the process; the first substantive obligation after registering is the annual return covering the mechanism's opening accounting period. The first UK CBAM accounting period runs the full 2027 calendar year, from 1 January 2027 to 31 December 2027, with the first return and payment due by 31 May 2028.
From 2028 onward, UK CBAM shifts to quarterly accounting periods, aligning the reporting rhythm more closely with ongoing import activity rather than a single year-end reconciliation. The table below sets out the confirmed dates.
| Period | Coverage | Return and payment due |
|---|---|---|
| First accounting period | 1 January 2027 to 31 December 2027 | 31 May 2028 |
| Q1 2028 | Quarterly period | 31 July 2028 |
| Q2 2028 | Quarterly period | 29 September 2028 |
| Q3 2028 | Quarterly period | 30 November 2028 |
| Q4 2028 | Quarterly period | 28 February 2029 |
Registration therefore needs to happen well before the first return is due. A business that registers in late 2027 under the extended deadline is still accountable for its full-year 2027 import activity when the first return falls due on 31 May 2028, so registering early gives more time to assemble embedded-emissions data from suppliers.
UK CBAM Registration vs EU CBAM Authorization
UK CBAM registration and EU CBAM's authorized declarant process share the same underlying purpose, establishing who is legally accountable for a carbon border obligation, but the mechanics differ in threshold design, administering body, and process. The comparison below highlights the differences most relevant to businesses trading in both markets.
- Threshold basis. UK CBAM uses a £50,000 value threshold tested two ways (backward and forward); EU CBAM uses a 50-tonne annual mass threshold per importer, described in the EU CBAM de minimis rules.
- Administering body. UK CBAM registration runs through HMRC's Government Gateway, a tax-administration system; EU CBAM authorization runs through the CBAM Registry and national competent authorities, covered in the CBAM authorized declarant guide.
- Process depth. EU CBAM authorization is a formal application with a statutory decision window; UK CBAM registration is closer to a standard HMRC tax registration, consistent with the UK mechanism's design as a direct tax rather than a certificate obligation.
Businesses importing covered goods into both the UK and the EU need to track both processes independently, since meeting one threshold has no bearing on the other. The UK CBAM vs EU CBAM comparison covers the full structural differences between the two mechanisms, and the UK CBAM and double payment analysis addresses the risk of carbon costs applying twice across UK-EU supply chains.
Frequently Asked Questions About UK CBAM Registration
How is the £50,000 UK CBAM threshold calculated?
The £50,000 threshold is calculated two ways, and meeting either one triggers a registration obligation. The backward-looking test, checked on the first day of each month, totals the value of CBAM goods that passed the tax point over the preceding 12 months. The forward-looking test, checked on any given day, forecasts the value of CBAM goods expected to be imported over the next 30 days. A business only needs to meet one test to become liable to register.
Do I have 30 days to register for UK CBAM?
Yes, in the standard case. Businesses normally have 30 days to register with HMRC once they meet either threshold test. The mechanism's first year carries an exception: any business that first becomes liable during 2027 has until 31 January 2028 to register, rather than the standard 30-day window. From 2028 onward, the standard 30-day deadline applies to newly liable businesses.
When can I actually register for UK CBAM with HMRC?
Registration will open through HMRC's Government Gateway, and as of July 2026 that is expected in the final quarter of 2026 (Q4 2026), later than the Q3 2026 date suggested by earlier coverage. HMRC has not published a confirmed opening date; the government's stated position is that final secondary legislation will be laid in autumn 2026, ahead of registration opening. Businesses should treat Q4 2026 as an indicative window rather than a confirmed date until HMRC issues guidance directly.
What happens if I import CBAM goods before I am registered?
Unregistered imports of covered goods do not escape the UK CBAM charge; the obligation to register does not create an exemption for imports made before registration is complete. HMRC applies its standard tax-administration penalty powers to registration failures, and the UK CBAM compliance guide sets out the full compliance sequence, including what to do if you realize you have crossed the threshold without registering.
Is the UK CBAM £50,000 threshold the same as the EU CBAM 50-tonne threshold?
No. They measure different things using different units, so a business's exposure under one does not translate directly to the other. UK CBAM tests a £50,000 value of covered imports two ways (backward-looking 12 months and forward-looking 30 days). EU CBAM tests a 50-tonne annual mass of covered goods per importer. A business trading in both markets needs to run both threshold checks independently, since crossing one threshold provides no information about proximity to the other.
What is the first return deadline after registering for UK CBAM?
The first UK CBAM accounting period covers the full 2027 calendar year, from 1 January 2027 to 31 December 2027, with the first return and payment due by 31 May 2028. This is a single annual period; from 2028 onward, UK CBAM moves to quarterly accounting periods with their own return deadlines.