If a UK buyer's monthly check shows it passed £50,000 weeks ago, when does its United Kingdom (UK) Carbon Border Adjustment Mechanism (CBAM) liability start?

HM Revenue and Customs (HMRC) words it two ways. Its policy summary says liability begins on the day the buyer ran the check. Its registration guidance says the buyer may be liable from the date its imports reached £50,000, and its own example uses that earlier date.

The £50,000 limit in plain words

Think of the limit as a tripwire. A UK buyer of CBAM goods adds up what it imports. Once the total reaches £50,000, it must register with HMRC.

The question is which day the buyer counts as the day it stepped over.

What HMRC says on each page

• Policy summary, backward looking test: on the first day of the month, a person looks back over the preceding 12-month period. "Where the test is met, the person's liability to register begins on the day they applied the test."
• Registration guidance: on the first day of each month, check whether you have imported £50,000 or more of CBAM goods in the previous 12 months. "If you have, you may be liable to register for CBAM from the date your imports met the £50,000 registration threshold."
• Our reading, not HMRC's: the two pages appear to describe the same monthly check but give different start dates when the imports crossed the line before the day of the check.

HMRC's own example, with the sums

The guidance example runs the check on 1 April 2028. The goods came in on 5 May 2027, 3 June 2027 and 1 January 2028. The guidance says their total value on 1 January 2028 is £70,000, and tells the importer: "You’re liable to register for the tax on 1 January 2028."

From 1 January 2028 to the check on 1 April 2028 is 91 days: 31 in January, 29 in February (2028 is a leap year) and 31 in March. So the example uses the earlier date, not the day of the check. The page does not print the value of each import, so we cannot show which one crossed £50,000.

Why the date matters (our reading, not HMRC's)

HMRC's summary says a liable person ordinarily has 30 days from the day they become liable to register. In the first calendar year of CBAM, businesses have until 31 January 2028. Failure to notify HMRC of liability is one of the penalty areas the summary lists.

If the earlier date is right, a buyer that finds the crossing late has less time left, or none. If the later date is right, the 30 days start at the check. The safe plan for a buyer is to count from the earlier date.

What an Indian supplier can do

• Ask your buyer which date it uses. A buyer that counts from the earlier date will chase your figures sooner.
• Keep dispatch and invoice dates for every UK shipment, so the buyer can show the week its 12-month total crossed the line.
• HMRC takes operational questions through its questions page. A buyer that is unsure can ask which wording applies.

HMRC's example dates, with the gap worked out

• Monthly check run on: 1 April 2028
• Imports in the 12 months: 5 May 2027, 3 June 2027, 1 January 2028
• Total value on 1 January 2028, as HMRC prints it: £70,000
• Liability date in the registration guidance: 1 January 2028
• Liability date if the policy summary wording is read alone: 1 April 2028
• Gap: 31 + 29 + 31 = 91 days

Dates and the £70,000 total are from HMRC's registration guidance example. The 91 days is our sum.

What Senseible does here

Senseible reads fuel invoices and electricity bills into dated, fingerprinted records. It does not file UK CBAM returns, work out your buyer's registration date or check commodity codes. Those stay with the importer and HMRC.

• Exactly £50,000: does it trigger registration?
• How the £50,000 value is counted
• When UK importers can register
• UK CBAM for Indian exporters

Sources: HMRC, Carbon Border Adjustment Mechanism (CBAM): Policy summary (updated 2 November 2026), HMRC, Work out the date you will need to register for CBAM (updated 16 July 2026), HMRC, Send HMRC questions about CBAM

Last reviewed 2026-11-07. The policy summary (updated 2 November 2026) and the registration guidance (updated 16 July 2026) differ on the start date. Re-read both when HMRC next updates either page. Our page on how the £50,000 value is counted (uk-cbam-threshold-customs-value) says liability starts on the day of the check; read it with this page.