CARF 2027.
Make your records explain the same activity.

What is CARF and why does May 2027 matter?

The Crypto-Asset Reporting Framework (CARF) is an OECD-designed regime that requires crypto exchanges to report customer activity to tax authorities. The UK activated CARF on 1 January 2026, and the implementing regulations are now final law (SI 2025/744). UK-serving exchanges must file their first reports, covering 2026 activity, with HMRC by 31 May 2027, including data on UK-resident users directly. HMRC plans to exchange information with participating jurisdictions by 30 September 2027. Once received, the structured exchange-side records can be compared with Self Assessment. The 2026/27 return, due 31 January 2028, is the first one HMRC can wholly cross-check against CARF data.

Which exchanges and platforms are covered?

CARF applies to centralised exchanges and custodial services that operate in or serve UK customers: Coinbase, Binance, Kraken, and around 50 UK-serving providers in total. The final UK rules use a control-based test rather than a blanket DeFi carve-out: a protocol or front-end with an identifiable controlling business can be a reporting entity, while genuinely autonomous protocols (Uniswap, Aave, Curve, etc.) have no one to file the report. In practice most DeFi activity stays outside the feed. However, exchange deposit and withdrawal records still let HMRC link wallets back to identified accounts, and on-chain activity is fully traceable from there.

What if my exchange filings don't match what I filed?

This is the central readiness question. Exchanges report gross activity (every buy, sell, swap, deposit, and withdrawal) without applying UK tax rules. Your Self Assessment should reflect the same activity after Section 104 pooling, same-day and 30-day matching, transfers between your own wallets, and DeFi events the exchange never saw. If those two pictures don't reconcile, HMRC may open an enquiry. Recomputing your gains under HMRC rules now lets you confirm or amend your return before the data arrives.

What should I actually do before May 2027?

Pull the relevant transaction history across exchanges and wallets, recompute the gains under Section 104 pooling, and compare the calculation with the figures already filed for open tax years. If you identify an error, the appropriate route may be an amendment, a disclosure, or adviser-led handling. Prompted status and penalty treatment depend on the facts and should not be assumed from CARF timing alone.

How far back can HMRC go once they have CARF data?

CARF does not itself change HMRC's statutory assessment time limits. The applicable period depends on the tax, filing history, behaviour, failure-to-notify rules, and whether offshore matters are involved. Four-, six-, twelve-, and twenty-year limits can arise in different circumstances, so multi-year cases should be scoped from the facts rather than a marketing summary.

Does ChainTax cover the DeFi side that CARF doesn't?

Yes. CARF covers reporting providers. ChainTax combines exchange and supported DeFi history, with 34 protocol-specific detectors across Ethereum, Arbitrum, Optimism, Base, and Polygon, plus CSV imports for Coinbase, Binance and Kraken; Crypto.com App (beta); plus Koinly universal CSV (compatible format). Connected sources feed the same cross-platform Section 104 pool.

How much does it cost to get a CARF-ready report?

Free up to 200 transaction records account-wide. £49 Light sets account-wide capacity at 2,500 records and £99 Active at 10,000; each one-time purchase unlocks report access for its selected tax year. If you need multiple report years, you pay per year, with a 2-year bundle option. Concierge above 10,000 account-wide records is quote-first, typically £249–£449.

What's not yet public about CARF in the UK?

Less than there used to be. The implementing regulations are final law (SI 2025/744), the data schema is the OECD's CARF XML schema, the first UK reports are due by 31 May 2027, and HMRC plans international exchange by 30 September 2027. Still settling: exactly how HMRC will operationally cross-match the feed against Self Assessment returns, when each overseas record will be available for operational use, and whether reporting expands to controlled DeFi front-ends in later phases. We update this page as guidance lands.