Tool
A worked example from invoice to tax due
Law as at 13 September 2026.
Every figure below that is not a rule of law is invented. The sectoral domestic price, the default value, the mill's emissions and the carbon price abroad are illustrative, because none had been published on 13 September 2026, and the reader should replace each with the real figure when it is available. The steps, the provisions and the arithmetic are the part to keep.
The consignment
The consignment is 500 tonnes of hot-rolled steel coil, net weight, bought from a mill outside the United Kingdom for £400,000 on the invoice. It is declared for free circulation at a Great Britain port on 14 May 2027 by a customs agent acting on behalf of the importer, a UK company that has already crossed the registration threshold. The commodity code begins 7208.
Steps one to four: caught, liable, weighed and priced
Chapter 72 is listed in Schedule 16 and 7208 is not excepted, so the coil is a CBAM good, mapped by Table 1e of the System Boundaries Document to iron or steel products. The declaration was made on the company's behalf, so under section 146(2)(a)(ii) the company is the importer; it is registered, so section 147(1) does not exclude the charge. The good was imported on 14 May 2027, in the quarter from April to June 2027 and in the accounting period that runs for the whole of 2027. The net weight on the declaration is 500,000 kilogrammes, supported by the mill certificate and the weighbridge ticket, so the weight is 500 tonnes. Suppose the Treasury has published the iron and steel price for that quarter as £20 per tonne of carbon dioxide equivalent.
| Route | Emissions | Tax before relief |
|---|---|---|
| Default value (illustrative 2.5 t per tonne) | 500 x 2.5 = 1,250 t | 1,250 x £20 = £25,000 |
| Verified data, integrated mill (1.90000 t per tonne) | 500 x 1.9 = 950 t | 950 x £20 = £19,000 |
| Mixed route, re-roller with default slab (2.16667 t per tonne) | 500 x 2.16667 = 1,083 t | 1,083 x £20 = £21,660 |
The default route
With no verified data, regulation 4 of SI 2026/995 gives the emissions as the weight multiplied by the default value. Suppose the default for heading 7208 is 2.5 tonnes per tonne: 500 multiplied by 2.5 is 1,250 tonnes, and section 149(1) gives the tax as £20 multiplied by 1,250, which is £25,000. The return states the level of the default value used, and no verification report is needed.
The verified data route
The mill has verified data for 2026, which regulation 9(2) allows for a good imported before 1 January 2028. It is an integrated works making its own sinter, pig iron and crude steel, so the precursors are part of the good and step 5 is omitted. The verification report states relevant emissions of 1,140,000 tonnes from goods under heading 7208 in 2026 and production of 600,000 tonnes. Step 7 divides to give 1.90000 tonnes per tonne, and step 8 multiplies by 500 to give 950 tonnes. The tax is £19,000, and the difference of £6,000 is the price of the data. Had the data arrived after a return filed on the default value, paragraph 8(2) of Schedule 17 would have prevented any amendment.
The mixed route
Suppose instead the mill is a re-roller with verified data for its own rolling only: 60,000 tonnes of emissions, 600,000 tonnes of coil, and 620,000 tonnes of slab bought from a works with no verified data. Under regulation 7(b) the slab carries the default value, say 2.0 tonnes per tonne, so step 5 adds 1,240,000 tonnes to give 1,300,000. Step 7 gives 2.16667 tonnes per tonne, step 8 gives 1,083 tonnes after rounding, and the tax is £21,660. The slab works' silence costs the importer £2,660 on this consignment against the fully verified route.
Carbon price relief
Suppose the mill's country runs an emissions trading scheme that meets regulation 6 of SI 2026/809 and the mill has supplied form CarbonVP1. From the form the importer calculates an effective carbon price of, say, £5 per tonne after free allowances and conversion. Regulation 13(1) gives the relief as £5 multiplied by 950 tonnes on the verified route, which is £4,750, within the cap of the liability. The tax due on the consignment is £19,000 less £4,750, which is £14,250.
The return, the payment and the file
The £14,250 joins the tax on every other covered consignment declared in 2027, each at the price for its own quarter, on the return for the period ending 31 December 2027, due with the payment before the end of 31 May 2028. The file holds the declaration with the code, date, value and net weight; the evidence of origin; the verification report; and the form with the working for the relief, all kept until the end of 2033.
What did not enter the calculation
The invoice value of £400,000 mattered for the registration threshold and for nothing else. The emissions of the power station behind the mill did not enter, because the System Boundaries Document maps direct emissions only. Of the £25,000 the consignment would have cost on the default route with no relief, the importer's own preparation removed £10,750. Chapter 8 of UK CBAM for Importers sets out every step with its provision.