CryptoTax UK · Guide
Crypto Self Assessment in the UK — a complete walkthrough
If you've disposed of crypto in the 2025/26 tax year, HMRC may expect you to declare it through Self Assessment. This guide walks you through registering, calculating your numbers, filling each box, paying any tax due and keeping evidence. Educational only — always confirm with a qualified accountant.
Run my Self Assessment numbers →Do I actually need to file?
You may need to register for Self Assessment if your total disposal proceeds for the year exceeded £50,000 (the reporting threshold for 2025/26 onwards), or if your gains after losses exceeded the £3,000 annual exempt amount, or if you have other crypto-related income like staking. If you're already in Self Assessment for any reason, crypto disposals typically go on the return regardless of size.
Key deadlines for 2024/25 returns
The 2024/25 tax year (6 April 2024 – 5 April 2025) has a 5 October 2025 registration deadline, a 31 October 2025 paper filing deadline and a 31 January 2026 online filing deadline. Tax owed is typically due by 31 January 2026 too. The same calendar shifts forward by 12 months for 2025/26.
Step 1: Register for Self Assessment
If you've never filed before, register at gov.uk/register-for-self-assessment. You'll receive a Unique Taxpayer Reference (UTR) by post within ~10 working days, then activation codes for your HMRC Online Services account. Set this up well before the deadline — you cannot file without a UTR.
Step 2: Run your numbers
Gather all disposals and acquisitions across exchanges and wallets. Apply HMRC's same-day, 30-day and Section 104 matching rules to calculate gains and losses per disposal. Total them, apply the £3,000 annual exempt amount, then apply the appropriate CGT rate based on your overall income. Free calculators (including ours) automate the matching engine.
Step 3: Fill in the right boxes
For 2024/25 onwards, crypto disposals go on SA108 boxes 13.1–13.5 (the new Cryptoassets section): number of disposals (13.1), total proceeds (13.2), allowable costs (13.3), gains before losses (13.4), losses in the year (13.5). Crypto income (staking, mining, paid airdrops) goes on the SA100 main return — typically box 17 for miscellaneous income. The CryptoTax UK SA108 helper outputs the exact numbers per box.
Step 4: Pay any tax due
Tax owed is typically due by 31 January following the end of the tax year. Pay via HMRC online, bank transfer or Direct Debit. Late payment may attract interest from 1 February plus a 5% penalty after 30 days. If you cannot pay in full, HMRC's Time to Pay arrangement may help — contact them as early as possible.
Step 5: Keep evidence for at least 6 years
HMRC may open an enquiry up to 6 years after filing (longer for deliberate errors). Keep CSV exports from every exchange you used, screenshots of wallet balances at year-end, your calculation spreadsheet or PDF accountant pack, and any correspondence with HMRC. The CryptoTax UK accountant pack bundles all of this into a single PDF.
Frequently asked questions
What if I missed a previous year's filing?
You may be able to file a late return, amend an existing one (within 12 months of the deadline), or use HMRC's Digital Disclosure Service for older years. Penalties may apply but typically reduce if you come forward voluntarily. Consider speaking to a qualified accountant if multiple years are affected.
Can I file the SA108 online without paper forms?
Yes — the entire Self Assessment, including SA108, can be filed via HMRC's online service. Third-party tax filing software may also support it. Either way, you'll need the same numbers our SA108 helper calculates.
What if I have crypto losses to carry forward?
Losses must be claimed within 4 years of the end of the tax year in which they arose. Claim them on SA108 (typically in the 'Losses available to be carried forward' fields) even if you don't have offsetting gains in the year — you cannot use a loss in a future year that you never reported.
Do I still need an accountant if I use a calculator?
For straightforward situations (a few exchanges, mainly BTC/ETH, no DeFi or NFTs), a calculator may be sufficient. For complex situations — mining as a trade, DeFi liquidity, multiple non-UK residencies, business activity, or large estates — a qualified UK tax adviser is typically worth the cost.
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Run my Self Assessment numbers →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.