How to Report
Crypto to HMRC.

Crypto gains go on the Capital Gains Summary pages, known as SA108. This is a supplementary form attached to your main SA100 Self Assessment return. You don't fill in SA108 separately — it's a section within the online filing system.

The form asks for four headline figures: total proceeds from all disposals, total allowable costs, total gains before losses, and total losses. You do not list every individual transaction on the form itself. HMRC wants the summary. Your transaction-level records are kept separately and produced if HMRC opens an enquiry.

In practice, if you made ten or fewer disposals in the year, you can enter them individually using HMRC's online system. For more than ten, you aggregate to the four summary figures and attach a schedule or spreadsheet if asked.

Step 1: Register for Self Assessment.If you've never filed before, go to gov.uk and register. HMRC will send your Unique Taxpayer Reference (UTR) by post within 10 working days. You need this before you can file. Register by 5 October following the end of the tax year you need to report — so for the 2024/25 tax year (ending 5 April 2025), register by 5 October 2025.

Step 2: Gather your transaction records.Pull export files from every exchange and wallet you used during the year. Most major exchanges — Coinbase, Kraken, Binance — let you download a full transaction history as a CSV. You need dates, amounts, GBP values at time of transaction, and fees paid.

Step 3: Calculate gains using the pooling method.HMRC uses section 104 pooling. Each token type has its own pool with an average cost basis. When you dispose of tokens, your gain is the proceeds minus the proportionate pool cost. You also need to check the same-day rule and the 30-day rule before calculating from the pool. This is the step where dedicated crypto tax software — Koinly, CoinTracker, TaxBit — earns its cost.

Step 4: Log in to HMRC Online Services.Go to your Government Gateway account and select “Complete your tax return.” Select the Capital Gains Tax pages when asked which sections apply to you.

Step 5: Enter your summary figures on SA108. Enter total proceeds, total costs, gains before losses, and losses. If you also received crypto as income (staking, mining, airdrops), enter this in the Other Income section of the SA100 main return, not on SA108.

Step 6: Submit and pay. The online return calculates your tax liability automatically. You can pay by bank transfer, debit card, or direct debit. Payment is due by 31 January alongside the return.

HMRC expects you to keep records for at least 5 years and 10 months after the end of the relevant tax year. For the 2024/25 tax year (ending 5 April 2025), keep records until 31 January 2031.

For each disposal, you need to record: the date of acquisition and disposal, the token type and quantity, the sterling value at time of acquisition and disposal, the exchange or wallet used, any fees paid (which reduce your gain), and your calculation showing how the gain was arrived at.

For tokens received as income, you need the date received, the type and quantity, and the sterling value on the date received (this becomes your cost basis if you later dispose of the tokens).

Keep exchange account statements, wallet addresses, and any screenshots or confirmations showing transactions and prices. If you used a decentralised exchange or a hardware wallet, the record-keeping burden falls entirely on you — there is no platform to request a history from.

The UK tax year runs from 6 April to 5 April. For each tax year, the key dates are:

5 October: Deadline to register for Self Assessment if you are new to it. Miss this and you may also miss the later filing deadlines.

31 October: Deadline for paper Self Assessment returns. Almost nobody files on paper any more, but the option exists.

31 January: Deadline for online Self Assessment returns and payment of any tax owed. This is the date that matters. For the 2024/25 tax year, the deadline is 31 January 2026.

31 July:Deadline for second payment on account, if applicable. Payments on account apply if your tax bill exceeds £1,000 and less than 80% was collected at source. HMRC splits the following year's estimated bill into two advance payments.

HMRC's penalty structure is automatic and escalates quickly.

Day 1 (missed 31 January deadline):£100 fixed penalty, regardless of whether you owe any tax.

3 months late:£10 per day, up to a maximum of £900. Combined with the initial £100, you're at £1,000 before HMRC even looks at what you owe.

6 months late:An additional 5% of the tax owed, or £300 — whichever is greater.

12 months late:Another 5% of tax owed or £300. In cases where HMRC believes you deliberately withheld information, this rises to 70% or 100% of the tax owed.

For late payment (filing on time but paying late), HMRC charges 7.25% interest per year on the outstanding amount (based on the Bank of England base rate plus 2.5 percentage points, reviewed quarterly).

The Crypto-Asset Reporting Framework — CARF — is an OECD information-sharing standard that UK-regulated exchanges must comply with from 2026. It requires exchanges to report user transaction data directly to HMRC: names, addresses, transaction values, asset types, and proceeds.

This is the same model as the Common Reporting Standard (CRS) used for offshore bank accounts, which has already led to tens of thousands of disclosures and penalty notices in the UK. CARF extends that model to crypto.

In practice, HMRC will have your Coinbase, Kraken, or Binance.UK transaction history before you file your return. Discrepancies between what you report and what the exchange reports will trigger automated compliance checks.

The short version: the window for retrospective under-reporting is closing. HMRC's nudge letter campaign — which has already contacted thousands of crypto holders — is just the opening move. The full data infrastructure is being built around them.

Not all crypto receipts are capital. Staking rewards, mining income, and some airdrops are treated by HMRC as miscellaneous income, taxed at income tax rates (20%, 40%, or 45%) rather than CGT rates (18% or 24%).

Income is reported in the Other Income section of the SA100 return, not on SA108. The amount to report is the sterling value of the crypto on the date you received it. That same figure becomes your cost basis for CGT purposes if you later dispose of the tokens.

Worth knowing: if you receive a salary or freelance income in crypto, HMRC treats it the same way as cash income. It goes through PAYE if your employer pays it, or appears as self-employment income if you're self-employed. In either case, it is income tax, not CGT.