SA108 for crypto: UK Capital Gains Summary box-by-box guide 2026

UK crypto disposals are reported on SA108— the Capital Gains Summary supplementary page of the Self Assessment return. Crypto sits in the "other property, assets and gains" section, not in shares or property. This guide walks through the boxes, the working sheet HMRC expects, and how the figures connect to the main SA100.

Which form do I use for crypto?

SA108 overview

SA108 is two pages of summary boxes plus the obligation to attach a computation showing the working. It covers all your chargeable gains for the tax year — not just crypto. Sections include:

• Listed shares and securities
• Unlisted shares and securities
• Property and other assets and gains (where crypto sits)
• Losses and adjustments
• Other claims and elections

Each section asks for a small number of summary figures: number of disposals, total proceeds, total allowable costs, gains, and losses. The detail lives in the attached computation, not in the form itself.

Box-by-box: SA108 for crypto

For crypto, the relevant box numbers are in the "other property, assets and gains" section. The 2025/26 SA108 boxes are (numbering can shift slightly between tax years — check the current form on gov.uk):

Box 21 deserves a note. HMRC accepts the use of established price sources — exchange quotes, CoinGecko, CoinMarketCap — for converting crypto values to GBP. Ticking box 21 is the disclosure that your figures rely on those quoted rates rather than direct receipts. Almost every crypto investor ticks this.

The computation working sheet

SA108 is a summary; HMRC expects the detail. For crypto the computation should list every disposal with:

• Date of disposal
• Asset (BTC, ETH, USDC, NFT collection, etc.)
• Quantity disposed
• GBP disposal proceeds (gross of fees)
• Disposal fees (deducted from proceeds)
• Allowable cost (from same-day, 30-day or Section 104 pool)
• Gain or loss
• Matching rule applied

Tools like Koinly export this as a PDF automatically. Attach it to your online filing as supporting documentation, or keep it on file ready to send if HMRC asks.

For paper filers, the computation goes in with the SA108 itself. For online filers, gov.uk Self Assessment lets you enter free-text in the "additional information" section explaining your methodology — you can reference the attached PDF or paste a summary.

Losses brought forward

If you carried forward unused losses from previous tax years, they are entered separately. The relevant boxes are in the "losses and adjustments" section of SA108:

• Losses brought forward from earlier years (used this year)
• Losses brought forward (not yet used)
• Losses arising this year — set against current year gains
• Losses arising this year — to carry forward

Losses must have been notified to HMRC within four years of the end of the tax year in which they arose. If you missed that window, the loss is not usable. For crypto, the notification typically happens through the SA108 itself in the year the loss was crystallised — file the SA108 with the loss reported, even if no current-year gains exist to offset.

Order of relief: current-year losses are set against current-year gains first, AEA is then deducted, and any remaining loss carries forward. The £3,000 AEA cannot be carried forward — it's use-it-or-lose-it.

How SA108 connects to SA100

SA108 is a supplementary page; the master return is SA100. The SA108 net taxable gain after AEA flows into the SA100 capital gains box, where it's combined with your income to determine which CGT band applies.

Crypto income (staking, mining, airdrops) goes on SA100 directly:

• Box 17on SA100 page TR3 — "other taxable income". List the type of income (e.g., "crypto staking rewards") and the GBP amount.
• SA103S or SA103Fif you're running crypto activity as a self-employed trade — that's a high bar.

The full Self Assessment is then submitted as one package: SA100 + SA108 + any other supplementary pages relevant to your circumstances (SA105 for property income, SA106 for foreign, etc.).

Summary

Crypto goes on SA108in the "other property and assets" section. Tick box 21 (estimates) and box 22 if you have a negligible value claim. Attach a computation showing per-disposal working. Income from staking and mining goes on SA100 box 17, not on SA108.

For the underlying CGT maths, see how to calculate UK crypto CGT. For deadlines, see when to report. The full rulebook is in our UK crypto tax guide. HMRC's SA108 form and notes live at gov.uk/government/publications/self-assessment-capital-gains-summary-sa108.