CryptoTax UK · Guide
Amend Self Assessment for Crypto UK — HMRC Guide
Made an error in your crypto tax return? HMRC allows amendments within a set window. This guide explains how to correct crypto-related mistakes on your Self Assessment. Educational only — not tax advice.
Recalculate my crypto gains →The amendment window
You can amend an online Self Assessment return within 12 months of the original filing deadline. For 2023/24 (filed by 31 January 2025), the amendment deadline is 31 January 2026. After this window you need to write to HMRC or use HMRC's Voluntary Disclosure process.
How to amend online
Log in to HMRC's Self Assessment online service, navigate to your submitted return and select 'Amend'. You can update your capital gains figures, add missing disposals or correct incorrect values.
Underpaid tax from crypto errors
If your amendment results in additional tax owed, HMRC will charge interest from the original payment deadline. Voluntary disclosure before HMRC opens an investigation typically results in lower penalties.
Frequently asked questions
What if I missed the 12-month amendment window?
You can make an overpayment relief claim for up to 4 years after the end of the tax year. To correct an underpayment after the amendment window, use HMRC's Voluntary Disclosure service.
Will HMRC penalise me for correcting a mistake?
HMRC distinguishes between careless errors (lower penalties) and deliberate errors (higher penalties). Correcting a genuine mistake voluntarily before HMRC contacts you typically attracts lower or no penalties.
More UK crypto-tax guides
Ready to estimate your UK crypto tax?
Free calculator. No sign-up needed.
Recalculate my crypto gains →Educational guidance only. CryptoTax UK is not a regulated tax adviser and the information above does not constitute tax, legal or financial advice. Always confirm your specific position with HMRC or a qualified accountant before filing.