For years, a lot of crypto activity sat in a grey area. Some people declared their gains, many did not, and HMRC's ability to check was limited. That era is ending, and the mechanism ending it is called CARF.
What CARF actually is
CARF stands for the Crypto-Asset Reporting Framework. It is an international standard, designed by the OECD, that brings crypto into the same kind of automatic tax reporting that banks have used for years. The UK has adopted it in full.
From 1 January 2026, UK crypto platforms, meaning exchanges and custodial wallet providers, must collect detailed information about their users and their transactions, and report it directly to HMRC. The first reports are due to HMRC by 31 May 2027, covering the 2026 calendar year, and from 2027 that data starts being exchanged internationally between tax authorities.
Was my activity really invisible before?
Not as much as many people assumed. HMRC has been receiving data from some major exchanges since around 2021. What changes with CARF is the scale and the consistency: instead of occasional data from a few platforms, HMRC moves to a standardised annual feed from the whole regulated sector, both in the UK and, through international exchange, abroad.
What this means if you have undeclared gains
This is the part that matters. When HMRC receives CARF data and it does not match your Self Assessment return, the likely first step is a nudge letter: a prompt asking you to check your affairs and correct anything that is wrong. It is not a formal accusation, but it should never be ignored, because it means HMRC already holds information pointing at you.
The strategic point is simple. It is far better to come forward first, on your own terms, than to wait for a letter driven by data HMRC already has. Voluntary disclosures made before HMRC makes contact almost always attract lower penalties.
What to do now
- Reconcile your full transaction history across every exchange and wallet you have used.
- Work out whether any past years were under-declared or missed entirely.
- If they were, consider a voluntary disclosure before a nudge letter arrives.
- Get your current and future returns onto a clean, defensible footing.
None of this needs to be done alone, and it is very often less painful than people fear once the numbers are actually in front of you. If you want a clear read on your own position, that is exactly what we do.
This article is general information, not tax advice, and the rules can change. Please get in touch for advice on your own circumstances.