How the check and the cost estimate work
Two things happen when you run the tool: a threshold test that decides whether you are in scope, and a cost estimate. This page sets out the method for both, and is explicit about which numbers are official figures and which are clearly labelled placeholders pending HMRC publication.
The scope test: the £50,000 threshold
Registration is triggered when the value of the CBAM goods you import meets or exceeds £50,000. That is a rolling test with two limbs, both measured on the customs value of the goods (not on emissions or on the charge):
- Forward look, any day: on any given day, do you expect the total value of CBAM goods you will import over the next 30 days to meet or exceed £50,000.
- Backward look, first of the month: on the first day of each month, did the total value of CBAM goods imported over the preceding 12 months meet or exceed £50,000.
If either limb is met, you become liable to register. The free checker tests the value you give against £50,000, and flags a borderline zone just below it because a single large consignment can trip the 30-day forward look even when your annual total is lower. The paid report applies the test to your specific figures and dates the answer.
The cost estimate: embodied emissions times rate
The charge on your imports is, in essence:
embodied emissions (tCO2e) × CBAM rate (£ / tCO2e) − relief for any overseas carbon price already paid
The estimator builds this up in steps:
- Tonnes. If you give a tonnage we use it. If you give only a value, we divide it by a rough market price per tonne for the sector to get an approximate tonnage. That market price is a dated assumption you can override by entering tonnes directly.
- Embodied emissions. Tonnes multiplied by a default embodied-emissions factor for the good (tCO2e per tonne).
- Gross charge. Embodied emissions multiplied by the CBAM rate (£ per tCO2e).
- Overseas relief. Shown as a flag only. Where the goods come from a country that levies a carbon price (for example the EU ETS), relief may reduce the charge, but the estimate does not deduct a figure because the amount depends on your evidence.
- A band, not a point. We report a range (roughly the net figure multiplied by 0.6 and by 1.4) to be honest about the imprecision, never a single false-precision number.
Which numbers are official, and which are placeholders
This is the important part. The structure of the charge is confirmed in gov.uk policy documents. The numbers you multiply are not all published yet, so we never present a pending number as official:
| Constant | What we use | Status |
|---|---|---|
| Default embodied-emissions factor | An illustrative placeholder from public industry data | PLACEHOLDER. The official per-good HMRC default value is pending publication. |
| CBAM rate (£ / tCO2e) | An illustrative figure based on recent UK ETS price levels | ILLUSTRATIVE. The official rate is set quarterly; the government's example is expected Autumn 2026. |
| Market price per tonne | A rough, dated market assumption | ASSUMPTION. Used only to convert a value into tonnes; overridable by entering tonnes. |
| Overseas carbon price offset | 0% in the number, shown as a flag | FLAG ONLY. Relief may apply; we do not deduct an unverified figure. |
Every cost output on the site and in the report carries the caption "illustrative estimate, not the official figure, as at 12 July 2026". The constants live in a single configuration object so that, the moment HMRC publishes the official default values and the rate, we replace them in one place and re-date every figure. That is the whole point of the product: it stays current as the rules land.
General information, not tax or legal advice. The estimate is a planning aid to size the obligation, not a quote or a tax computation. Only HMRC guidance and the enacted legislation are definitive. Confirm your position with a qualified adviser before you rely on it.
Sources
Every rule we apply traces to a gov.uk policy document or the underlying legislation. The full list, with the status of each fact, is on the sources page, and the confirmed-versus-pending picture is kept live on the CBAM Rulebook Status board.