Do I need to file an SA108 for small crypto gains?

You must file the SA108 if your total disposal proceeds exceed £50,000 in the tax year, OR if your net gains exceed the £3,000 Annual Exempt Amount, OR if you're already filing a Self Assessment for any reason. When in doubt, file.

Which box on the SA108 is for crypto?

From the 2024/25 SA108 onwards, HMRC added a dedicated Cryptoassets section (boxes 14–22 in the standard form). For prior years, crypto was reported in the 'Listed shares and securities' or 'Unlisted shares and securities' section as appropriate.

Do I list every disposal individually?

Not necessarily — HMRC accepts a summary on the form with detailed working attached as a PDF/CSV. CryptoLens generates that backing report automatically.

How do I report crypto income (staking, airdrops)?

Crypto income goes on the SA100 (the main return), not the SA108. Box 17 'Other taxable income', with a brief description in the additional information box. Keep a year-end GBP total per income type.

Updated 26 April 2026 · 8 min read

SA108 Crypto: Step-by-Step Filing Walkthrough

Exactly how to fill in HMRC’s SA108 Capital Gains Summary for crypto disposals. Box-by-box for the new cryptoassets section. Worked example included.

Do you actually need an SA108?

You need to file the SA108 if any ONE of these is true for the 2025/26 tax year:

Total disposal proceeds exceed £50,000 (regardless of whether you made gains)
Net gains exceed the £3,000 Annual Exempt Amount
You’re registered for Self Assessment for any reason (employed + side income, dividends, rental property, etc.)
You want to register a capital LOSS to carry forward (you have 4 years to claim a loss after the year it arose)

If none of the above apply, you don’t need to file — but keep records anyway. HMRC can ask up to 6 years back.

The Cryptoassets section, box by box

The 2025/26 SA108 has a dedicated cryptoassets section. The boxes you’ll fill:

Number of disposals: total count of disposal transactions across the year. One disposal = one sell, swap, or spend event.

Total disposal proceeds: sum of GBP value received at the moment of each disposal.

Total allowable costs: sum of GBP cost basis (Section 104 pool average) per disposal, plus allowable expenses (gas fees, platform fees in GBP).

Total gains:sum of disposals where proceeds > cost (positive amounts only).

Total losses in the year:sum of disposals where proceeds < cost (positive amounts representing losses).

Total losses brought forward used:losses from prior tax years now used to offset this year’s gains.

Adjustments: usually leave blank unless you have specific items HMRC has told you to adjust for.

HMRC accepts a single line per token (summarised) OR per pool. They don’t require every individual swap on the form, but you must keep the underlying detail in your records and attach it as a supplementary document if your numbers are large or unusual.

The supplementary detail document

Attach a CSV or PDF with one row per disposal. Each row needs:

Date of disposal (YYYY-MM-DD)
Token disposed (e.g. ETH, USDC)
Quantity
Disposal proceeds in GBP
Cost basis in GBP (Section 104 pool average × quantity, OR same-day match, OR 30-day match)
Gain/loss
Match type used (Section 104, same-day, or 30-day)

CryptoLens generates this attachment automatically — paste your wallet, click “Generate SA108 PDF”, attach to your Self Assessment online filing.

Worked example: Sarah’s 2025/26 return

Sarah held ETH and SOL during 2025/26. Her year:

Aug 2025: sold 2 ETH, proceeds £8,000, Sec 104 cost £4,500. Gain £3,500.
Oct 2025: swapped 100 SOL for ETH; SOL value £15,000, Sec 104 SOL cost £8,000. Gain £7,000.
Feb 2026: sold 1 ETH at £4,200; Sec 104 ETH cost £2,400. Gain £1,800.

Totals:
Number of disposals: 3
Total proceeds: £27,200
Total costs: £14,900
Total gains: £12,300
Total losses: £0

Net gain: £12,300
Annual exempt amount: £3,000
Taxable gain: £9,300

CGT due (basic rate band): £9,300 × 18% = £1,674
(or £9,300 × 24% = £2,232 if higher rate)

Filing deadlines

Online filing: 31 January 2027 (for 2025/26 tax year)
Paper filing: 31 October 2026 (mostly relevant if HMRC has refused you online filing)
Pay any tax due: 31 January 2027
Payments on account (if Self Assessment tax > £1,000): 31 January and 31 July