What is CBAM? The carbon border, explained.

The Carbon Border Adjustment Mechanism (CBAM) is the European Union’s tool for putting a carbon price on imports of certain carbon-intensive goods — so that goods made outside the EU carry the same carbon cost as goods made inside it. It mirrors the EU Emissions Trading System (ETS) at the border, and its purpose is to stop carbon leakage: the risk that production simply moves to wherever emitting is cheapest.

What CBAM covers

CBAM applies to imports in six groups of goods, identified by their commodity (CN) codes:

• Iron & steel
• Aluminium
• Cement
• Fertilisers
• Hydrogen
• Electricity

For each import, what matters is the embedded emissions of the goods — the emissions released in producing them. CBAM looks at two parts: the direct emissions of the production process itself, and — for the goods CBAM counts it for, such as cement and fertilisers — the indirect emissions from the electricity used to make them. This is the embedded carbon of the imported goods, for the declaration — not a measure of your company’s wider emissions.

Who is responsible

The obligation sits with the importer of record in the EU — or, where an importer is established outside the customs territory, with an indirect customs representative acting on their behalf. In the definitive period, importers need to hold authorised CBAM declarant status to bring covered goods into free circulation.

That makes three groups the people who actually live with CBAM day to day:

1. Importers of CBAM goods, who carry the obligation and the cost.
2. Customs consultants, brokers and indirect representatives, who file for many importers at once.
3. Non-EU suppliers, whose production data decides how much their EU customers pay.

Default values and actual emissions

Here is the part that decides the bill. If you can prove the actual embedded emissions of the goods — using data from the producer’s installation — CBAM is calculated on that figure. If you can’t, CBAM applies a default value, set to a high, dirty-production assumption.

The gap between the two is real money. A cleaner producer’s actual emissions are usually well below the default, so proving them lowers both the certificate cost and the carbon recorded against the import. That is the mechanism working as intended: cleaner production, proven, costs less at the border.

Transitional vs definitive period

CBAM phased in over two stages:

• Transitional period — reporting only. Importers report the embedded emissions of their goods each quarter, in a defined XML format, with no charge yet.
• Definitive period — the financial obligation. Importers buy and surrender CBAM certificates against the embedded emissions of what they import, priced in line with the EU ETS.

The transitional period was about building the data discipline; the definitive period is when that data turns into a bill.

Why it matters now

CBAM is not a tax return you file once and forget. It is a per-line, per-shipment obligation tied to commodity codes, net mass and origin — the same fields on every customs declaration you already lodge. Getting it right means reading those declarations accurately, knowing the embedded carbon behind each line, and filing the exact format the registry accepts.

CBAM rules continue to evolve. This guide is kept current — check the “last updated” date above, and always confirm specifics against the official European Commission CBAM guidance for your situation.

Next: see CBAM default values and the markup for why proving actuals pays, or estimate your own liability with the free CBAM calculator.