UK CBAM guidance
UK CBAM deadlines: the dates to plan around
The first CBAM year is designed as a transition period. Recording starts on 1 January 2027; the first return and payment are due by 31 May 2028.
Last updated: 13 August 2026
Key dates
| Date | What happens | What to do |
|---|---|---|
| 1 January 2027 | UK CBAM starts. Threshold tests apply to imports passing the tax point from this date. | Begin keeping complete records of CBAM goods. |
| During 2027 | Monitor the £50,000 forward and look-back tests. | Keep a dated evidence trail of your calculations. |
| 31 January 2028 | Transition registration deadline for businesses that triggered registration in 2027. | Register if required; HMRC says registration opens by this date. |
| 31 May 2028 | First annual CBAM return and payment deadline, for the 2027 accounting period. | Submit and pay; the first return also needs the quarter of import for each good. |
What changes after the first year?
The first accounting period runs from 1 January to 31 December 2027. From 2028 the system moves to quarterly accounting periods, with return and payment deadlines set after each period. HMRC’s policy summary lists the transitional 2028 deadlines; use the official guidance for the latest dates.
Make the timetable operational
- Set a monthly threshold review on the first working day.
- Set a supplier-evidence chase cadence, well before the return preparation window.
- Freeze a quarterly import-data extract and reconcile it to customs records.
- Have tax, procurement and customs agree one pre-return review.
Important: a longer first filing window does not delay the date you need to collect import and emissions data. Records are needed from 1 January 2027.