HMRC crypto penalties, nudge letters and CARF fines explained
Quick answer: Late Self Assessment triggers automatic penalties from £100. Inaccuracy penalties range from 0% to 100% of tax depending on behaviour. CARF can fine you up to £300 for not giving your NI number to a UK crypto provider. If you get an HMRC nudge letter about crypto, check your records and respond — do not ignore it.
HMRC can charge penalties and interest on unpaid crypto tax. Since 2019 it has used exchange data for compliance campaigns. From 2026, CARF adds more data. This guide explains what to expect and what to do.
Late filing and payment penalties
Missing the 31 January Self Assessment deadline starts at £100, rising with further delays. Late payment accrues interest and penalties. Set a calendar reminder for 6 April (tax year end), 5 October (register), and 31 January (file and pay).
Inaccuracy and failure to notify
Underpaying because of careless errors or failing to register for Self Assessment when required can lead to penalties of 0% to 30% of tax (careless) or higher if deliberate. Keeping good records supports a ‘reasonable care’ defence.
HMRC nudge letters
HMRC sends letters when exchange data suggests undeclared gains. A nudge is an opportunity to review and correct — use the voluntary disclosure service if tax is owed. Ignoring letters can escalate to formal enquiry.
CARF penalties from 2026
Failure to provide required personal and tax information to UK crypto service providers under CARF can result in an administrative penalty up to £300. Providers must collect data from 1 January 2026.
What to do if you receive contact from HMRC
Do not panic. Gather records, compare against exchange statements, and seek professional help for large amounts. Respond within deadlines. If tax is owed, calculate interest and consider voluntary disclosure.
Frequently asked questions
Can HMRC see my DeFi wallet?+
On-chain activity is not reported under CARF like exchange data, but you remain legally required to declare taxable events.