File Crypto Tax on Your UK Self Assessment 2025/26

The 2025/26 tax year ended on 5 April 2026. If you bought, sold, swapped, staked, or earned crypto at any point between 6 April 2025 and 5 April 2026, this is the return that covers it. The online filing deadline is 31 January 2027, but the calendar that actually matters starts months earlier: people who need to file for the first time must tell HMRC by 5 October 2026, normally by registering for Self Assessment. HMRC says telling it after that date could lead to a penalty.

2025/26 is the second tax year to use the dedicated crypto boxes on SA108 (boxes 13.1 to 13.8). It is also the first tax year to use the post-Autumn-Budget CGT rates of 18 percent and 24 percent throughout, with no split-year complication. That last point matters more than it sounds: most online guides you find right now will be 2024/25 content with the year number swapped, and they will tell you to fill Box 51 for the rate adjustment. That split-year adjustment does not apply to 2025/26.

This guide walks through the full process. Who needs to file, the deadlines that catch people out, the calculation rules, the SA100 and SA108 box entries, and the DeFi-specific gotchas that generic crypto tax guides miss. It is written for both first-time filers and people who filed last year and want to know what changed.

Who needs to file Self Assessment for 2025/26

Capital gains can be reported through Self Assessment or HMRC's Capital Gains Tax service. If you are already registered for Self Assessment, include the crypto capital-gains pages when either of the following applies:

• Your total capital gains across all chargeable assets (crypto, shares, property other than your main home) exceeded the £3,000 annual exempt amount in 2025/26
• Your total disposal proceeds exceeded £50,000, even if your gains were below the exempt amount.

If you are not registered, the £50,000 proceeds threshold alone does not require a return. You still need to tell HMRC about chargeable gains above the annual exempt amount. Self Assessment may also be required if:

• You earned crypto income (staking rewards, lending interest, airdrops you actively claimed, mining rewards) above the £1,000 trading and miscellaneous income allowance
• Your other income or circumstances require a return under HMRC's Self Assessment rules

The £1,000 trading and miscellaneous income allowance applies across relevant trade and miscellaneous income; it is not a separate allowance for each staking platform or side activity. Full relief may apply where total relevant gross income is no more than £1,000, subject to the eligibility rules. The allowance is optional and cannot be combined with deducting actual expenses for the same income.

For more detail on the threshold tests, see do I need to report crypto to HMRC?

The five dates that matter for 2025/26

Most guides only mention the 31 January deadline, but four other dates are load-bearing for 2025/26 filers:

The 5 October registration deadline is the one that catches first-time crypto filers. HMRC has been issuing nudge letters to suspected non-filers throughout 2026. Separately, in-scope providers began collecting user and transaction data under CARF on 1 January 2026, with their first reports due between 1 January and 31 May 2027. If a nudge letter has already landed, see our HMRC letter response guide. It's separate from the filing deadline above; follow the date and instructions on the letter. If you want to prepare for the 2027 reporting cycle before any letter arrives, the CARF 2027 readiness page sets out what to reconcile.

Step-by-step: from registration to submission

Step 1: Register for Self Assessment (first-time filers only)

Use HMRC's current Self Assessment registration service. HMRC says the service launched on 9 September 2026 can issue your Unique Taxpayer Reference to your online account within 72 hours. Register early enough to resolve any account or identity checks before the filing deadline.

For crypto-only filers (no other reason to be in Self Assessment) you register as 'not self-employed'. The return type is the standard SA100 with the SA108 capital gains supplement.

Step 2: Gather your records

HMRC expects you to keep records in pounds sterling for every transaction. The minimum dataset:

• Date of every acquisition and disposal
• Asset type (token contract address for ERC-20s, NFT collection address for NFTs)
• Number of units transacted
• GBP value at the moment of the transaction
• Wallet addresses involved
• Running balance of your Section 104 pool for each asset

Exchange CSV exports cover most of this for centralised exchange activity. For DeFi, you need on-chain transaction hashes plus a pricing source for each token at each timestamp. Most centralised exchange exports use FIFO, which is wrong for HMRC, so you have to recalculate on a Section 104 basis. See why your Coinbase report is not enough and how to handle Binance trades for HMRC.

Step 3: Calculate your gains and income

This is where most filers either spend a weekend in spreadsheets or use a UK crypto tax calculator. The mechanics are covered in the next section, but the output you need is two numbers per tax year: total taxable capital gain (after losses, after annual exempt amount) and total crypto-related miscellaneous income.

Step 4: Fill SA100 and SA108

SA100 is the main return. Crypto income (staking, lending, and airdrops whose service/trade facts make them taxable) goes in the 'Other taxable income' section with a brief description, for example 'crypto staking rewards: £1,200'.

SA108 is the capital gains supplement, and since 2024/25 it has dedicated crypto boxes 13.1 to 13.8. The next section covers what goes in each.

Step 5: Submit and pay

File online via your Government Gateway account before 31 January 2027. The system calculates your tax liability automatically from the boxes you fill. Pay via bank transfer, debit card, or direct debit. HMRC's sort code and account number for Self Assessment payments are listed on the gov.uk payment page. Double-check them before sending.

The HMRC rule: Section 104, same-day, B&B, then SA108

UK CGT on crypto uses three matching rules in a fixed order, defined by section 104 of the Taxation of Chargeable Gains Act 1992:

1. Same-day matching. If you bought and sold the same asset on the same day, those transactions match against each other first.
2. 30-day bed and breakfasting rule. Disposals match against any acquisitions of the same asset in the 30 days immediately following the disposal.
3. Section 104 pool. Anything left over uses the weighted average cost basis of all your remaining holdings of that asset.

You apply these rules per asset symbol, not per wallet or per exchange. All your USDC across Coinbase, Binance, MetaMask, and a Ledger sit in the same pool. Same for ETH, same for every other token.

For the deep mechanics of how these rules interact, see Section 104 pooling explained and the same-day and 30-day rules.

Once you have a list of disposals with their matched cost bases, the SA108 boxes are straightforward. Boxes 13.1 to 13.8 are dedicated to cryptoassets:

For the full breakdown of every box including worked numbers, see SA108 boxes 13.1 to 13.8 explained. It follows the current form and notes, including the claim or election code in box 13.6.

Worked example: a 2025/26 DeFi filer's return

DeFi-specific gotchas for 2025/26

Generic Self Assessment guides assume centralised exchange-only activity. If you used DeFi at any point in 2025/26, these four classification areas need explicit evidence rather than a generic transaction label:

Bridge treatment depends on what changed

A supported same-owner, same-asset USDC bridge can carry basis where beneficial ownership and the token rights are preserved. HMRC CRYPTO22110 says cross-ledger treatment depends on the facts, so different-token output and incomplete destination evidence need review. See is bridging crypto taxable in the UK?

Direct ETH and WETH wraps can carry basis

ChainTax applies basis-carry treatment to a direct decoded ETH to WETH wrap where beneficial ownership and economic exposure are preserved. Do not extend that result automatically to wstETH, receipt tokens, or other wrappers with different rights. See wrapped tokens and UK tax.

Taxable staking rewards can create income, then CGT later

Where a staking reward is taxable miscellaneous income, its GBP fair market value on receipt is reported on SA100 and becomes cost basis in the Section 104 pool. A later disposal is considered separately for CGT. The reward arrangement and whether the activity amounts to a trade still matter. See how to report staking rewards to HMRC and DeFi income vs capital gains.

Liquidity pool entries and exits are composite events

Adding tokens to a Uniswap V2 or V3 LP position is a disposal of those tokens (entering the pool) and an acquisition of the LP position. Removing liquidity reverses it. The income earned (LP fees) is a third event, taxable as miscellaneous income. A catch-all rule can miss the LP token entirely or treat the whole flow as a single swap. See how HMRC taxes Uniswap LP positions.

2025/26 vs 2024/25: the Box 51 difference

The most common mistake on 2025/26 returns will be people copying their 2024/25 SA108 entries verbatim and filling Box 51 again. Box 51 was the split-year CGT rate adjustment. It existed because the Autumn Budget 2024 changed the main CGT rates from 10/20 percent to 18/24 percent on 30 October 2024, mid-way through the 2024/25 tax year. Disposals before the boundary were taxed at the old rates and disposals after at the new rates, so a manual adjustment was required.

For 2025/26 the entire tax year applies the new 18/24 percent rates. There is no split-year rate boundary. Box 51 is not a routine crypto total, although a separate adjustment listed in the current SA108 notes may still apply to particular facts.

For the current form, see the 2025/26 SA108 crypto box-by-box guide for the exact boxes, supporting computation, and worked example.

How ChainTax handles your 2025/26 return

ChainTax applies UK matching rules to supported activity and keeps unresolved classifications, incomplete source history and missing taxable prices visible for review:

1. Centralised exchange and DeFi in one place. Import Coinbase, Binance, and Kraken CSVs alongside on-chain activity from Ethereum, Arbitrum, Optimism, Base, and Polygon. All disposals of the same asset land in one Section 104 pool, as HMRC requires.
2. Section 104 with same-day and 30-day matching. Each recognised disposal is matched against same-day acquisitions, then 30-day bed and breakfast acquisitions, then the S104 pool, in that order. Each match is shown explicitly so you can trace the calculation, while unresolved activity remains visible for review. Classified as Disposal, Income, or Transfer with confidence ratings.
3. Bridges, wraps, and LP positions use evidence-specific rules. Supported same-owner, same-asset bridges and direct ETH/WETH wraps can carry basis where ownership and economic exposure are preserved. Different-token outputs and incomplete destination evidence remain review items. Supported LP entries expose the relevant economic legs rather than treating the transaction as a generic transfer.
4. Staking rewards split across SA100 and SA108. Staking, lending interest, and airdrops confirmed as taxable are recognised as Income at fair market value on the receipt date, with that value becoming the cost basis for subsequent disposals.
5. SA108 box values pre-calculated for 2025/26. Boxes 13.1 to 13.8 are produced with reviewable working. The report keeps the totals and supporting calculation together so you can review them before entering the relevant figures in your filing software.

Supported classifications and unresolved review states are traceable. You can paste any transaction hash into the public explainer to see the available classification evidence before you sign up; unsupported or incomplete activity may remain visibly unresolved.

Not sure which tool to file with? You can compare the leading UK crypto tax tools before you commit.