For UK crypto investors before May 2027
UK CARF reporting started 1 January 2026. The first automatic data exchange between HMRC and other tax authorities is expected from May 2027. The practical question for every UK investor is whether your Self Assessment will reconcile against what your exchange reports.
Free up to 200 transactions. Pay only when you download the report.
1 Jan 2026
UK CARF live
Around 50 UK-serving exchanges began collecting CARF-shaped data on customer activity. The reporting period now runs.
May 2027
first exchange
The first automatic data exchange between HMRC and other tax authorities is expected. From that point HMRC has a feed it can match against returns.
Lower penalties
if you act first
Voluntary correction before HMRC raises the question consistently lands in a lower penalty band than being asked. The reconciliation is cheapest done early.
Why CARF matters for your return
Exchanges report gross activity. Every buy, sell, swap, deposit, and withdrawal is sent to HMRC with your name, address, and tax identifier attached. There is no UK tax logic in that feed.
Your Self Assessment shows the net taxable position — after Section 104 pooling, after same-day and 30-day matching, after transfers between your own wallets, after DeFi events the exchange never saw, and after gas fees on disposals.
Those two pictures should describe the same person. When they don't — because gross activity looks much larger than net disposals, or because the exchange-side history references years you didn't file for — HMRC can open an enquiry. Reconciling now means you either confirm everything ties up, or you find the gap and correct it before the question lands in your inbox.
Which path is mine?
Pick by transaction count and activity type. Most retail investors land in the first column.
Most common
Under 10,000 transactions
Coinbase, Binance, Kraken plus some DeFi. Run it yourself.
Above the cap
Over 10,000 transactions
High-volume DeFi, multi-wallet, NFT activity. We run the sync for you.
Specialist needed
Trade or business activity
Mining as a trade, company crypto, large undisclosed positions.
Already received an HMRC nudge letter?
The 60-day clock is the binding constraint, not CARF. Start at /hmrc-letter — the same self-serve / Concierge / accountant routing, shaped around the deadline rather than the readiness window.
If self-serve fits
CEX and DeFi in one Section 104 pool
The reconciliation only works if exchange disposals and on-chain disposals share the same average-cost pool. Most spreadsheets and single-surface tools split them — ChainTax pools them.
Same-day → 30-day → S104, in HMRC order
The matching rules HMRC requires, applied per disposal. 2024/25 split-year CGT (10/20% before 30 Oct, 18/24% after) handled automatically.
Show Working — full audit trail
Every disposal records the matching rule, the S104 pool snapshot before and after, and the price source with confidence rating. If HMRC asks for working under a CARF-driven enquiry, you have it.
Multi-year reconciliation
Each tax year is a separate report; loss carry-forward is automatic across years. Bundle 2 years for a £19–£29 saving on a multi-year reconciliation.
How it works
Sign up and add your wallets
Public addresses only — never private keys or exchange API keys. Add Coinbase, Binance, or Kraken via CSV import in the same flow.
The engine sorts every transaction
Disposals, income, transfers, liquidity — across Ethereum, Arbitrum, Optimism, Base, and Polygon. 33 protocol-specific detectors plus pattern matching and a generic-swap fallback.
Compare against what you filed
The summary surfaces total disposals, taxable gains, income, and SA108 box mapping per year. Hold those next to your filed Self Assessment for each open year and the reconciliation is direct.
Confirm or amend, before May 2027
If the figures match, no action needed. If they don't, the PDF + CSV gives you the working to amend a return or file a voluntary disclosure with full evidence.
An honest note on CARF specifics
Confirmed
Still settling
The reconciliation itself doesn't depend on those open questions. Your Self Assessment either reflects the activity HMRC can see, or it doesn't — that's the work, and it's the same work whichever schema lands.
We update this page as official guidance is published.
No tax tool is perfect. Here's what ChainTax cannot yet handle automatically — and what you should check manually or discuss with your accountant.
Full detail: How it works → Known limitations
FAQ
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. The first automatic data exchange between HMRC and other tax authorities is expected from May 2027, covering 2026 activity. From that point forward, HMRC will receive a structured feed of exchange-side records — names, addresses, tax IDs, and transaction history — that it can match against your Self Assessment.
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. DeFi protocols (Uniswap, Aave, Curve, etc.) are not reporting entities under CARF. 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 your full transaction history across exchanges and wallets, recompute the gains under Section 104 pooling, and compare against the figures already on your Self Assessment for open tax years. If everything reconciles, no action is needed. If you find missed disposals, unreported income, or under-stated gains, voluntary correction or disclosure before HMRC raises the question typically lowers the penalty band by a wide margin. Coming forward unprompted is consistently treated more leniently than being asked.
How far back can HMRC go once they have CARF data?
HMRC's standard look-back is four years for innocent error, six years for careless behaviour, and up to twenty years for deliberate non-disclosure. CARF doesn't change those windows — it gives HMRC much better source material for opening an enquiry within them. Most retail investors' full crypto history sits inside the look-back, which is why the practical question is reconciliation across all years on file, not only 2026 onwards.
Does ChainTax cover the DeFi side that CARF doesn't?
Yes. CARF covers exchanges. ChainTax covers exchanges and DeFi together — 33 protocol-specific detectors across Ethereum, Arbitrum, Optimism, Base, and Polygon, plus CSV imports for Coinbase, Binance, Kraken, and Koinly. The same Section 104 pool spans CEX and on-chain disposals, which is the part most tools and spreadsheets get wrong.
How much does it cost to get a CARF-ready report?
Free up to 200 transactions. £49 for Light (up to 2,500 per tax year) or £99 for Active (up to 10,000). One-time payment per tax year — if you need multiple years for a clean reconciliation, you pay per year, with a 2-year bundle option. Concierge sync (we run it for you, over 10k transactions) is quote-first, typically £249–£449.
What's not yet public about CARF in the UK?
The exact schema HMRC will receive, the precise timing of the first exchange, and whether DeFi reporting expands in later phases are all still being finalised through HMRC and OECD guidance. The reporting obligation itself, the 1 January 2026 commencement date, and the May 2027 first-exchange window are confirmed. We update this page as guidance lands.
Background reading: the full guide to CARF and what it means for UK investors.
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ChainTax is a tax calculation tool and does not provide tax, financial, or legal advice. Verify your figures with a qualified adviser before filing.