How does HMRC know about my crypto?
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In short: Crypto exchanges share customer data with HMRC, and from 2026 the UK adopts the OECD Cryptoasset Reporting Framework (CARF), under which platforms must report users' transactions automatically. HMRC also sends 'nudge' letters to suspected crypto holders.
HMRC already obtains data directly from UK and overseas crypto exchanges through information requests, and it has run several rounds of 'nudge' letters to people it believes hold cryptoassets, prompting them to check whether they owe tax.
From 2026, the UK is implementing the OECD's Cryptoasset Reporting Framework (CARF). Reporting cryptoasset service providers must collect and report user identity and transaction information, with the first exchanges of data between tax authorities due to follow. In practice this means HMRC will increasingly receive automatic, structured data on disposals.
Because gains and income may have built up over several years, anyone who has not declared crypto can use HMRC's voluntary disclosure service. Declaring before HMRC makes contact almost always results in lower penalties than waiting to be found.
Primary source: gov.uk/government/publications/tax-on-cryptoassets