HMRC's first CBAM guidance: spend 2027 keeping records

In mid-July 2026 HMRC published its first proper guidance on the UK carbon border tax — a set of pages on registration, record-keeping and carbon price relief. Most of the coverage focused on the deadlines. The most important sentence was quieter: "Registration for CBAM will open by 1 January 2028." The tax starts on 1 January 2027. For up to a year, importers will be liable for a tax they cannot yet register for, and HMRC's instruction for that gap is explicit: keep records so that you can register and file "when the facility becomes available".

That single line reorganises what year one actually is. Not a filing year. A records year.

The calendar, corrected

Until July, most people (us included) expected registration to open in late 2026. The official position, from the registration guidance collection, is:

• 1 January 2027 — liability begins; the statutory £50,000 threshold tests run from this date.
• By 1 January 2028 — HMRC's registration service opens.
• 31 January 2028 — deadline to register for anyone who triggered the threshold during 2027 (unchanged; this easement now makes sense — it exists because the doors open late).
• 31 May 2028 — first return and payment, covering all of 2027.

If you trigger in March 2027, you register ten months later and file fourteen months later — on data you either kept or didn't.

The records list

HMRC's keeping-records guidance sets out what a liable importer must retain, for six years from the later of creation or the end of the accounting period. Read as a job description for 2027, it says: for every import of covered goods, be able to produce —

• the 8-digit commodity code and description;
• the import date and tax point (normally the customs entry acceptance date);
• valuation and weight documents — the customs value drives the £50,000 test, the weight drives the charge;
• proof of origin — a new duty in the made regulations, pointing at the non-preferential rules of origin;
• evidence for any exemption claimed: private use, UK-origin goods, returned goods relief, temporary admission;
• if you report actual rather than default emissions, the verification report or summary from the supplier's independent verifier;
• if you claim carbon price relief, the carbon pricing scheme documentation and relief calculation — in practice, the Carbon Pricing Verification Form;
• the quarter in which each good passed the tax point (once returns are quarterly), and any repayment claim details.

Most of that is customs data your broker already holds. Two items are not: the supplier's verification report and the carbon-price form. Those come from overseas installations, through conversations you have to start, on timelines you don't control. They are the reason "keep records" is not the same as "file your broker's exports in a folder".

What registration will ask for

The same guidance wave confirmed the particulars the registration service will collect, matching the made Administrative Provisions Regulations: your EORI number, VAT registration number if registered, business details, the date you triggered registration, and — the one that surprises people — an estimate of the weight of CBAM goods you expect to import in the next twelve months, per sector. Weight, not value, because the tax is charged per tonne of embodied carbon. Nobody has that number lying around; it comes from the same ledger you should be keeping.

What this means in practice

The threshold is a monthly test, not a one-off. The backward-looking test runs on the first day of every month over the preceding twelve; the forward-looking test can trigger any day you expect to exceed £50,000 in the next thirty. The trigger date is a registration particular and determines your deadline. Testing once in January and forgetting about it is how people discover in May 2028 that they triggered in March 2027.

Defaults are the fallback; the data decides the bill. A return filed on default values cannot be amended to actual supplier data afterwards. Whatever verified data you have collected by the end of 2027 is the data your first return is built on. The chase has to run through the year.

Relief is evidence, not entitlement. HMRC's official list of qualifying carbon pricing schemes (27 August) includes the EU ETS and China's national ETS — but relief follows the effective price actually paid, attested on the official form by an independent verifier, kept with your records.

The tools, mapped to the list

We built CBAMReturn around exactly this guidance, so the mapping is direct:

• The liability preview reads a broker's ledger export, runs the statutory threshold test, prices every line with its working shown, and ends with a registration pack — trigger date, estimated per-sector weights, the checklist — ready for whenever HMRC opens the doors.
• A free founding account keeps that ledger, re-runs the threshold test on the first of every month and emails you the position, and holds a per-supplier chase board for the two record types that don't come from your broker.
• The supplier data template and the carbon price relief kit are the two asks you send upstream — the verification report and the carbon-price form — phrased so that suppliers understand why answering keeps their goods competitive.

HMRC told importers to keep records for a year before they can even register. It is, unusually, advice that gets more valuable the earlier you take it.