How to Report Crypto Tax in the UK Online (2026): SA108, CARF Data-sharing and What HMRC Will Ask

Last updated: 18 May 2026

Understanding how to report crypto tax in the UK online has never been more important than it is right now. Since 1 January 2026, the OECD’s Crypto-Asset Reporting Framework (CARF) has required crypto exchanges and other reporting platforms to share detailed user transaction data directly with HMRC. The practical effect is that HMRC can now cross-reference the disposals and income on your Self Assessment return against the records it receives from platforms, making unreported crypto activity far easier to detect. This guide walks through every step of the online reporting process, from registering for Self Assessment and calculating your gains to completing the SA108 capital gains pages and knowing exactly what HMRC will ask if it contacts you.

This article is general information only and does not constitute legal or tax advice. Individual circumstances vary, consult a qualified tax professional before making decisions about your tax position.

Quick Answer, Do I Need to Report Crypto Tax in the UK?

If you are a UK tax resident and you have disposed of cryptoassets or received crypto income during a tax year, you will almost certainly need to declare it to HMRC through Self Assessment. Here is the 60-second summary:

• Capital Gains Tax (CGT) applies when you sell crypto for GBP, swap one token for another, use crypto to pay for goods or services, or give it away (other than to a spouse or civil partner). Each of these counts as a “disposal.”
• Income Tax applies when you receive cryptoassets as payment for work, earn staking or mining rewards, or receive certain airdrops, the sterling value at the date of receipt is taxable income.
• Which forms? Report capital gains on the SA108 (Capital Gains Summary) supplementary pages. Report crypto income on the relevant sections of the SA100 (the main Self Assessment return).
• Key deadline: For the tax year ending 5 April 2026, the online Self Assessment filing deadline is 31 January 2027.
• CARF note: HMRC now receives transaction-level data from crypto platforms, so it can identify undeclared disposals.
• Annual exempt amount: If your total chargeable gains from all assets (not just crypto) fall within the CGT annual exempt amount, you may not owe CGT, but you may still need to report the disposals if total disposal proceeds exceed four times the annual exempt amount.

What Changed in 2026, CARF and HMRC Crypto Reporting

The biggest shift in crypto tax UK 2026 compliance is the activation of the Crypto-Asset Reporting Framework. CARF is an international standard developed by the OECD that requires crypto-asset service providers, exchanges, brokers, and certain DeFi front-ends that qualify as reporting entities, to collect and report detailed information about their users’ transactions to the relevant tax authority. In the UK, that authority is HMRC.

What Data Do Platforms Report Under CARF?

Under CARF, reporting crypto-asset service providers must collect and share the following categories of information with HMRC:

• Account holder identity. Full name, address, date of birth, jurisdiction of tax residence, and taxpayer identification number (such as a National Insurance number for UK residents).
• Self-certification. Platforms must obtain a self-certification from each user confirming their tax residence, similar to the CRS process for bank accounts.
• Transaction details. The type, volume, and value of crypto-asset transactions, including exchanges for fiat, crypto-to-crypto swaps, and transfers, broken down by transaction category.

The result is that HMRC’s visibility into individual crypto activity is now comparable to its visibility into bank interest or share dealing through existing automatic exchange mechanisms.

Timeline, Key Milestones Leading to 2026

Industry observers expect the January 2027 filing window to be the first occasion on which HMRC systematically matches Self Assessment returns against CARF-reported data at scale. Taxpayers who have historically under-reported should treat this as an urgent prompt to review prior years.

Which Crypto Events Are Taxed, CGT vs Income Tax (With Examples)

Before you can report crypto to HMRC, you need to classify each transaction correctly. HMRC’s published guidance draws a clear line between events that give rise to crypto capital gains UK obligations and those that create crypto income tax UK liabilities.

Capital Gains Tax Events (Disposals)

A “disposal” for CGT purposes occurs whenever you:

• Sell cryptoassets for fiat currency (GBP, EUR, USD, etc.)
• Swap one cryptoasset for another (e.g., exchange ETH for BTC)
• Use cryptoassets to pay for goods or services
• Give cryptoassets away (except to a spouse or civil partner)

Income Tax Events

Income Tax is charged on crypto received as:

• Wages or salary paid in crypto by an employer
• Staking or validator rewards (where you are not carrying on a trade)
• Mining rewards (whether treated as trading income or miscellaneous income)
• Airdrops received in return for a service or as part of a marketing engagement

Comparison Table, Tax Treatment and Reporting Forms

Worked Example, Capital Gains Calculation

Suppose you bought 2 ETH in March 2023 for £2,400 (£1,200 each). In January 2026, you sell 1 ETH for £3,100. Your calculation under section 104 pooling would be:

• Disposal proceeds: £3,100
• Allowable cost: £1,200 (the pooled cost per unit, £2,400 ÷ 2)
• Gain: £3,100 − £1,200 = £1,900

If the same-day rule or the 30-day “bed and breakfasting” rule applies (because you also acquired ETH on the same day or within 30 days of the sale), those acquisitions must be matched to the disposal first, before the section 104 pool is used. Getting this sequencing wrong is one of the most common errors in self assessment crypto reporting.

How to Report Crypto Tax in the UK Online, Step-by-Step (SA108 + SA100)

This section provides a detailed walkthrough of how to report crypto to HMRC using the online Self Assessment system. Follow each step in order.

Step 1, Registering for Online Self Assessment

If you have never filed a Self Assessment return before, you must register with HMRC first:

1. Go to the GOV.UK Self Assessment registration page and select the reason you need to file (e.g., “capital gains” or “other income”).
2. You will receive a Unique Taxpayer Reference (UTR) by post, this typically takes 7–10 working days.
3. Set up a Government Gateway account (or sign in if you already have one) and link it to your UTR.
4. You will then be able to access the Self Assessment online service and start your tax return.

Plan ahead, do not leave registration until close to the crypto tax deadline. If you register too late, you may miss the 31 January online filing deadline and face automatic penalties.

Step 2, Preparing Your Transaction Dataset

Before you open the online return, assemble a complete record of every crypto transaction in the tax year (6 April to 5 April). You will need:

• Exchange CSV exports. Download transaction histories from every platform you used (Coinbase, Binance, Kraken, etc.). Ensure the exports include dates, amounts, and fiat values.
• Wallet transaction logs. For any on-chain activity through non-custodial wallets, use a block explorer or crypto tax tool to extract a full log.
• GBP valuations. HMRC requires disposal proceeds and acquisition costs in sterling. Record the GBP value at the date and time of each transaction, using a consistent and reputable pricing source.
• Supporting documents. Keep receipts, invoices, or screenshots for any purchases made with crypto, gifts given, or income received.

Third-party tools such as Koinly, CoinTracking, and Blockpit can automate the aggregation and GBP conversion of exchange and wallet data. However, you remain legally responsible for the accuracy of the figures on your return, a software output is not a defence if the underlying data is wrong.

Step 3, How to Calculate Disposals and Allowable Costs

HMRC requires you to apply specific matching rules when calculating crypto capital gains UK figures:

1. Same-day rule. If you acquire and dispose of the same type of cryptoasset on the same day, the acquisition is matched to the disposal first.
2. 30-day (“bed and breakfasting”) rule. If you re-acquire the same cryptoasset within 30 days after a disposal, the new acquisition is matched to that disposal rather than being added to the pool.
3. Section 104 pool. All remaining tokens of the same type are held in a single “pool.” The allowable cost of each disposal is calculated using the average cost per unit across the pool.

Apply these rules in order, same-day first, then 30-day, then pool, for every disposal in the tax year. This is the sequencing that catches most people out, especially where they are buying and selling the same token frequently.

Step 4, Entering Figures Into SA108 (Box-by-Box Guidance)

When you access the SA108 Capital Gains Summary pages in the online return, the following fields are the key entries for crypto disposals:

If you have more than a small number of disposals, you will typically report summary totals in the SA108 boxes and keep the detailed transaction-by-transaction computation (spreadsheet or tax tool report) in your records. HMRC can request the detailed computation at any time.

Where to put crypto income on SA100: Staking rewards, mining income, or airdrops treated as miscellaneous income should be entered in the “Other UK income” section of the SA100 main return. If your mining or crypto-related activity amounts to a trade, use the self-employment pages (SA103S for turnover below £85,000, or SA103F otherwise).

Step 5, Submitting and Paying

1. Review every section of your return. The HMRC online system will calculate your total tax liability, including any CGT due.
2. Submit the return electronically, you will receive an online confirmation with a submission reference.
3. Pay any tax owed by 31 January after the end of the tax year. Payment methods include direct debit, bank transfer (Faster Payments or CHAPS), or debit/credit card through the HMRC online portal.

Borderline case, trading as a business: If HMRC considers your crypto activity to be trading (e.g., high-frequency, systematic buying and selling for profit), your gains may be taxed as trading income rather than capital gains. This is a fact-specific determination. If there is any doubt, professional advice is essential before you file.

What HMRC Will Ask If They Contact You, Practical Checklist

With CARF now in effect, HMRC crypto reporting capabilities mean the tax authority can match platform-reported data against individual Self Assessment returns. If HMRC identifies a discrepancy, or if you have not filed at all, it will contact you. Here is what to expect and how to prepare.

How HMRC Typically Makes Contact

• “Nudge” letter. A letter stating that HMRC has information suggesting you may have disposed of cryptoassets and inviting you to check your tax position.
• Formal enquiry or information notice. An enquiry under section 9A TMA 1970 (into a filed return) or a standalone information notice requesting specific documents.
• Online notification. A message in your Personal Tax Account or HMRC app alerting you to review your position.

What HMRC Will Typically Request

Based on published HMRC guidance and professional experience in this area, the following checklist covers the documents and information HMRC is likely to ask for:

• Source of funds. How did you acquire your initial crypto holdings? (bank transfers, P2P purchases, gifts, income)
• Exchange and wallet records. Full transaction histories from every platform and wallet used, including deposit and withdrawal records.
• KYC / identity verification. Copies of identification documents used to open exchange accounts.
• Dates and values of all disposals. A complete schedule showing each disposal, the GBP value at the time, and the basis of that valuation.
• Gain/loss computations. Your working calculations showing how you applied the same-day, 30-day, and pooling rules.
• Bank statements. Records showing fiat deposits to and withdrawals from exchanges, as well as any crypto-to-fiat proceeds received into bank accounts.
• Third-party tool reports. If you used software (Koinly, CoinTracking, etc.), the generated tax reports and CSV files.
• Explanation of any discrepancy. If your return does not match the platform-reported data, HMRC will expect a clear, documented explanation.

How to Respond

1. Do not ignore the correspondence, a failure to respond can lead to penalties and the use of HMRC’s information powers.
2. Gather the requested documents promptly. Use a structured format: one folder per exchange, a master spreadsheet of disposals, and a cover letter summarising your position.
3. If you realise you have made errors or omissions, consider making a voluntary disclosure (see below) before HMRC escalates the enquiry, a prompted disclosure attracts higher penalties than an unprompted one.
4. Take professional advice before responding if the amounts involved are significant, the transactions are complex, or you are unsure whether your original return was correct.

Common Mistakes and How to Avoid Them

Errors in how to report crypto tax in the UK online are widespread. These are the issues that most frequently lead to incorrect returns, and HMRC scrutiny:

• Missing historical exchange data. Exchanges may close, de-list accounts, or limit CSV export periods. Download and back up your data regularly, do not assume it will always be available.
• Incorrect GBP valuations. Using a price from the wrong time of day, a different exchange, or failing to convert from USD to GBP at the correct exchange rate. Always document the exact price source and timestamp.
• Ignoring the pooling rules. Treating each purchase as a separate lot (FIFO or LIFO) rather than using the mandatory same-day / 30-day / section 104 pooling hierarchy.
• Misclassifying income as capital gains. Staking rewards, mining income, and service-linked airdrops are income, not capital gains. Reporting them on SA108 instead of SA100 understates Income Tax and may overstate CGT losses.
• Double counting. Reporting transfers between your own wallets or exchanges as disposals when they are not. A transfer to your own wallet (with no change of beneficial ownership) is not a disposal.
• Forgetting crypto-to-crypto swaps. Every token swap is a disposal. If you exchanged BTC for a stablecoin, that is a taxable event, even though you never received GBP.
• Not claiming losses. Losses can be offset against gains in the same year and carried forward. Failing to report them means you may overpay tax.

Red flags that are likely to trigger HMRC review include large disposal proceeds with no corresponding SA108 entry, significant deposits into bank accounts from exchange platforms with no declared gains, and CARF-reported data that does not match your return.

When to Get Professional Help or Make a Voluntary Disclosure

While many straightforward crypto disposals can be self-reported, certain situations demand professional advice. Consider engaging a specialist tax adviser or lawyer if:

• You have complex transaction chains involving DeFi protocols, liquidity pools, wrapped tokens, or yield farming.
• You hold crypto across multiple jurisdictions and need to determine where tax residence applies or whether double tax treaties are relevant.
• You have significant undeclared gains from prior tax years.
• You have received a letter or enquiry from HMRC relating to crypto.
• Your activity may cross the line from investment into trading (which changes the tax treatment entirely).

The Voluntary Disclosure Route

HMRC maintains a specific digital disclosure facility for cryptoassets. The GOV.UK page “Tell HMRC about unpaid tax on cryptoassets” allows taxpayers to notify HMRC that they have undeclared tax liabilities relating to crypto and to make a disclosure. The process works as follows:

1. Notify HMRC. Submit a notification that you intend to make a disclosure.
2. Prepare your disclosure. Calculate the tax owed for each affected year, including interest.
3. Submit and pay. Send the full disclosure and arrange payment of the outstanding tax, interest, and any applicable penalties.

An unprompted disclosure, one made before HMRC contacts you, will generally attract lower penalties than a prompted disclosure made after HMRC has already raised questions. With CARF data now flowing into HMRC systems, early indications suggest the window for making a genuinely unprompted disclosure is narrowing. Where users of crypto exchanges or platforms covered by CASP regulations have not previously declared UK tax, addressing this proactively is strongly advisable.

Practical Resources and Templates

The following official resources are essential references when you report crypto tax in the UK online:

• HMRC cryptoassets guidance: Check if you need to pay tax when you sell cryptoassets, the primary GOV.UK guidance page covering CGT, income, and reporting obligations.
• HMRC voluntary disclosure: Tell HMRC about unpaid tax on cryptoassets, the official page for notifying and making a disclosure.
• HMRC CARF guidance: Check if you’ll need to report cryptoasset data to HMRC, platform obligations and data fields.
• OECD CARF overview: Crypto-Asset Reporting Framework, the international standard and implementation timeline.
• Transaction record template: Prepare a spreadsheet with columns for: date, transaction type (buy/sell/swap/receive), token, quantity, GBP value at transaction date, exchange or wallet, counterparty token (for swaps), and notes. This format maps directly to the SA108 summary fields.

For a broader view of the regulatory environment facing crypto businesses and operators, see our guides on crypto licensing requirements and international compliance frameworks.

Conclusion, How to Report Crypto Tax in the UK Online Without Mistakes

The 2026 tax year marks a turning point for UK crypto tax compliance. CARF data-sharing has eliminated the information gap that previously existed between taxpayers and HMRC, and accurate self assessment crypto reporting is now essential. To get it right: collect every transaction record, classify each event as either a capital gain or income, apply the correct matching rules, complete the SA108 and SA100 online, and keep your working papers for at least six years. If your situation is complex or you have undeclared liabilities from prior years, seek specialist advice before HMRC makes contact. For help finding a qualified tax professional, visit the Global Law Experts lawyer directory.

Sources

1. GOV.UK, Check if you need to pay tax when you sell cryptoassets
2. GOV.UK, Tell HMRC about unpaid tax on cryptoassets
3. GOV.UK, Check if you’ll need to report cryptoasset data to HMRC (CARF implementation)
4. OECD, Crypto-Asset Reporting Framework (CARF)
5. UK Parliament, Written question on CARF implementation (HL13368)
6. Koinly, How to report crypto to HMRC
7. CoinTracking, UK Crypto Tax Forms Guide
8. LITRG, Cryptoassets and tax