CBAM Returns: Filing and Deadlines

UK CBAM uses a phased approach to return frequency. From 2027 to 2029 inclusive, returns are filed annually. From 2030 onwards, returns become quarterly.

The annual return covers the calendar year (1 January to 31 December). The filing deadline is 31 January of the following year. For example, the 2027 return must be filed by 31 January 2028.

Once quarterly returns begin in 2030, each quarter covers a three-month period ending 31 March, 30 June, 30 September, and 31 December. Returns are due one month after the quarter end.

Each CBAM return must include:

• Total quantity of each covered product imported (by CN code, net weight in tonnes)
• Total embedded emissions for each product (tonnes CO₂e)
• Emissions intensity used for each product (tonnes CO₂e per tonne of product)
• Source of emissions data (verified supplier, unverified supplier, default value)
• Total carbon price paid in the country of origin (if claiming relief)
• Total CBAM liability in GBP (after any relief claimed)

The return is a declarative document. You are certifying that the information is accurate and complete to the best of your knowledge. HMRC may audit your return and request supporting evidence.

Unlike VAT, CBAM returns cannot be amended after filing. Any error discovered after the deadline stands until the next period. This makes accuracy and completeness essential.

CBAM returns are filed through HMRC's online service. The process is expected to work as follows:

• Log in to Government Gateway and navigate to the CBAM service
• Select the reporting period and entity
• Enter product-by-product data: CN code, net weight, emissions intensity, emissions
• Declare any carbon price relief being claimed
• Review and submit the return
• Receive a submission reference number for your records

HMRC has confirmed there will be no CBAM API for the initial years of the regime. This means you cannot file automatically — figures must be transcribed from your calculation system into the government portal.

Oremly produces a return-ready summary in HMRC field order. Every figure is linked to its supporting evidence, making transcription accurate and auditable.

HMRC has a range of enforcement powers for CBAM non-compliance:

• Late filing: Initial penalty of £100, escalating for persistent delays
• Inaccurate returns: Penalty based on the amount of underpaid liability, calculated using HMRC's standard penalty framework
• Failure to register: Separate penalty for not registering within 30 days of exceeding the threshold
• Interest: Late payment interest accrues on unpaid CBAM liability from the due date

The penalty regime is designed to incentivise compliance rather than punish errors. HMRC has said it will take a proportionate approach, particularly in the early years. However, intentional non-compliance or reckless under-reporting can attract significant penalties.

HMRC requires importers to retain all records supporting CBAM returns for six years from the filing date. This includes:

• Copies of all CBAM returns filed
• Supplier emissions data and correspondence
• Emissions calculations and methodology documentation
• Import ledgers and customs declarations
• Any evidence supporting carbon price relief claims
• Records of default value usage and reasons

Oremly's evidence store automatically retains every document and links it to the return it supports. The append-only audit log provides a tamper-evident record of every action taken.