HMRC now sees your crypto: what CARF means for your CGT
From 1 January 2026, UK exchanges and other cryptoasset service providers have to collect data on every user and hand it to HMRC. It is called the Cryptoasset Reporting Framework, the UK’s version of an OECD standard that more than 60 countries have signed. The first report lands at HMRC by 31 May 2027, covering all of calendar year 2026. So HMRC will soon hold a record of your disposals straight from the source, and your Self Assessment has to line up with it.
The timeline
Your provider has to obtain a valid self-certification from you confirming who you are and where you are tax resident. If you do not give it, the provider can be penalised up to £300 per user, so expect exchanges to chase you with forms and to freeze functionality until you respond. Give them false or careless information and the penalty can fall on you instead.
What HMRC actually receives
| What the exchange sends | Detail |
|---|---|
| Your identity | Name, date of birth and home address. |
| Tax residence | Country of residence, plus your National Insurance number or Unique Taxpayer Reference if you are UK resident. |
| Transaction totals | For each disposal: value, the type of cryptoasset, the type of transaction and the number of units. |
Notice what is missing. The exchange reports the gross value and units of each disposal, but it does not hold your cost basis, and it cannot see coins you bought elsewhere and moved in. Nor does it apply the HMRC matching rules that turn proceeds into an actual gain. So the figure HMRC builds from raw exchange data sits much closer to your total proceeds than to anything you owe. If a prompt arrives quoting a big number, that number is almost never your tax bill.
The calendar-year trap
CARF reports run on the calendar year. UK Capital Gains Tax runs on the tax year, 6 April to 5 April. They do not align, so a single CARF report straddles two of your returns. Say you made two disposals during 2026:
| Disposal | Date | Proceeds | Your tax year | CARF report |
|---|---|---|---|---|
| Sold 1 BTC | 20 Feb 2026 | £50,000 | 2025-26 | Calendar 2026 |
| Swapped 10 ETH for SOL | 12 Aug 2026 | £28,000 | 2026-27 | Calendar 2026 |
Both sit in the one calendar-2026 report HMRC receives by 31 May 2027. But the February BTC sale belongs on your 2025-26 return (filed by 31 January 2027) and the August swap belongs on your 2026-27 return (filed by 31 January 2028). The ETH-to-SOL swap is itself a disposal even though no money changed hands, valued in GBP at the moment of the trade. If you mentally file “my 2026 crypto” as one block, you will put disposals in the wrong tax year and your figures will not reconcile against what HMRC holds.
What to do now
Do not wait for the exchange to tell you your gain. Confirm your self-certification details with each provider so your account does not get frozen, then build the numbers yourself: every disposal in GBP, matched under Same Day, the 30-day Bed and Breakfast rule and the Section 104 pool, split across the right tax years. The figure you put on your SA108 should hold up against the raw data HMRC will be sitting on, not come straight off an exchange dashboard.
That reconciliation is exactly what our calculator does: upload your trade history and it applies the HMRC matching rules to crypto the same way it does to shares, then hands you a per-disposal breakdown grouped by tax year. For the mechanics of pooling and swaps, see how UK crypto CGT calculations work, and for the return itself, the cryptoasset boxes on SA108.
Sources
- Implementation of the Cryptoasset Reporting Framework (CARF) – GOV.UK
- Collecting cryptoasset user and transaction data – GOV.UK
- Check if you need to report cryptoasset data to HMRC – GOV.UK
- The Reporting Cryptoasset Service Providers (Due Diligence and Reporting Requirements) Regulations 2025
- CRYPTO22100 – Crypto-to-crypto swaps are disposals