UK CBAM · Two tracks to 2028
UK CBAM runs on two tracks until 30 June 2028.
A transitory instrument modifies Schedule 17 to the Finance Act 2026 for the first eighteen months: different accounting periods, different deadlines, a different registration date. On 1 July 2028 the modification lapses and the standing rules apply unmodified.
Two tracks, one pivot
The Carbon Border Adjustment Mechanism (Transitory Provision) Regulations 2026 modify Schedule 17 to the Finance Act 2026. They have effect for charges to CBAM arising in the period beginning with 1 January 2027 and ending with 30 June 2028, and for returns in respect of accounting periods ending with or before that date.
SI 2026/830 reg 1(3) to (4)The modification lapses. Accounting periods are the periods of three months ending at the end of March, June, September and December. Return and payment are both due before the end of the last working day of the second month after the accounting period ends.
FA 2026 Sch 17 paras 6(2), 6(3), 7(2)The dated rail
- 1 Jan 2027UK CBAM applies
Part 5 of the Finance Act 2026 has effect in relation to goods imported into the United Kingdom on or after 1 January 2027.
FA 2026 s.158(1) - 1 Jan — 31 Dec 2027First accounting period
Twelve months, not a quarter. The transitory instrument substitutes a single 2027 period beginning with 1 January 2027 and ending with 31 December 2027.
SI 2026/830 reg 2(3) · Sch 17 para 6(2)(a) - 31 Jan 2028Registration deadline for 2027 triggers
For a person who triggers registration in 2027, the standing 30-day window is replaced by a fixed date: 31 January 2028.
SI 2026/830 reg 2(2) · Sch 17 para 2(4) - 31 Mar 2028Second accounting period ends
The period beginning with 1 January 2028 and ending with 31 March 2028. Return and payment are both due before the end of 31 July 2028.
SI 2026/830 reg 2(3) and 2(4) - 31 May 2028First return, first payment
Both fall due for the 2027 accounting period before the end of 31 May 2028 — five months after that period closed.
SI 2026/830 reg 2(3) and 2(4) · Sch 17 paras 6(3), 7(2) - 30 Jun 2028Third accounting period ends
The period beginning with 1 April 2028 and ending with 30 June 2028. Return and payment are both due before the end of 29 September 2028 — the date is written into the instrument, not calculated from it.
SI 2026/830 reg 2(3) and 2(4) - 30 Jun 2028The pivot — modification lapses
The transitory modification stops here. It reaches charges arising up to and including 30 June 2028, and returns for accounting periods ending with or before that date. Nothing after it is modified.
SI 2026/830 reg 1(3) to (4) - 1 Jul 2028 onwardStanding quarterly rhythm
Accounting periods are the three-month periods ending at the end of March, June, September and December. Return and payment are both due before the end of the last working day of the second month after the period ends.
FA 2026 Sch 17 paras 6(2), 6(3), 7(2)
Transitory against standing
Twelve months for 2027, then two quarters in 2028 — 1 January to 31 March, and 1 April to 30 June.
Three months, ending at the end of March, June, September and December.
Fixed dates written into the instrument: 31 May 2028, 31 July 2028, 29 September 2028.
Before the end of the last working day of the second month after the accounting period ends.
31 January 2028, for a person who triggers registration in 2027.
Before the end of 30 days beginning with the day the person first triggered registration.
What triggers registration
A person must register with HMRC if the person triggers registration. Schedule 17 sets two limbs and either is enough. Both are measured on the aggregate value of CBAM goods imported into the United Kingdom in the course of a business.
£50,000Both conditions must hold: it is the first day of the month, and during the preceding 12 months the person imported CBAM goods into the United Kingdom, in the course of a business, with an aggregate value of £50,000 or more.
FA 2026 Sch 17 para 2(2)(a)The person is expected to import CBAM goods with an aggregate value of £50,000 or more before the end of a period of 30 days.
FA 2026 Sch 17 para 2(2)(b)A person who triggers registration must register before the end of the period of 30 days beginning with the day on which the person first triggered registration. For a 2027 trigger, that window is replaced by 31 January 2028.
FA 2026 Sch 17 para 2(4) · SI 2026/830 reg 2(2)Not yet settled
How emissions embodied in CBAM goods are to be determined and evidenced is left to regulations, which may also require information to be verified by a specified person or body. The three CBAM instruments made in July 2026 — SI 2026/802, SI 2026/809 and SI 2026/830 — are made under other powers.
FA 2026 Sch 17 paras 10(1) and 10(2)(h)The Act defines emissions embodied in a CBAM good as emissions attributable to its production, then leaves the meaning of attributable — including emissions from activities carried out in connection with production — to Treasury regulations. Until those are made, the treatment of indirect emissions is not fixed.
FA 2026 s.148(1) to (3)UK CBAM · Prepare the data
Your first UK return is due 31 May 2028. The data behind it starts accruing 1 January 2027.
Carbon Mandate prepares the declaration data behind the obligation. You register and file with HMRC.