Reporting crypto on your Self Assessment sounds intimidating, but it comes down to filling in the right boxes on form SA108. Get the figures right and it is a straightforward process — the difficulty is calculating those figures correctly, not the filing itself.
Do you need to complete SA108?
You need to complete the Capital Gains Summary (SA108) if:
- —Your total capital gains exceed the £3,000 annual exempt amount
- —Your total disposal proceeds from all assets exceed £50,000 in the year
- —You want to report losses to carry forward against future gains
If you are below both thresholds and have no losses to report, you do not need SA108 — but keep records for at least six years.
Box-by-box guide to SA108
The sum of all gains before any losses or allowance are deducted. Include gains from all assets — crypto, shares, property.
Enter as a positive number. All losses from disposals in the current year.
Losses from earlier years that you are using to reduce this year's gain. Only use as many as you need.
£3,000 for 2024/25 and 2025/26. Enter the full £3,000 if your net gain (after losses) exceeds this.
Box 3 minus boxes 4, 5, and 6. This is the figure you pay CGT on. Cannot be negative — if it would be, enter zero.
Box 7 × 18% (basic rate) or 24% (higher/additional rate). If you are a basic rate taxpayer but the gain pushes you into higher rate, split accordingly.
Crypto income: different form, different treatment
Staking rewards, mining income, and crypto received as payment are not capital gains. They are income, reported on the SA100 main return under “Other income.” If you mix them up — reporting staking income on SA108 as a capital gain — both forms will be wrong and your tax liability will be incorrect.
If you have both staking income and crypto gains in the same year, you need to complete both SA100 (for the income part) and SA108 (for the capital gains part).
The most common mistakes on SA108
- —Using FIFO instead of HMRC's matching rules (same-day, 30-day, Section 104 pool)
- —Missing crypto-to-crypto swaps — only reporting GBP sales
- —Forgetting to declare losses — missing the carry-forward benefit
- —Including staking income in box 3 instead of reporting it separately as income
- —Using the wrong CGT rate — check whether the gain pushes you into higher rate
Polyconomic's SA108-compatible PDF report labels every figure with the corresponding box number. Download your report →
Frequently asked questions
Can I file SA108 online or does it have to be on paper?
Both are possible. Most people file online via HMRC's Self Assessment portal, which includes the Capital Gains Summary section. The paper SA108 form is also accepted. The online system calculates the tax due automatically once you enter the figures.
What is the difference between SA100 and SA108?
SA100 is the main Self Assessment tax return covering income, employment, and other income sources. SA108 is the Capital Gains Summary supplement, attached to SA100. You need SA108 specifically for capital gains. Staking and mining income goes on SA100, not SA108.
I have disposals on multiple exchanges. Do I list each one separately on SA108?
No. SA108 asks for aggregate totals — total gains, total losses, not a breakdown by exchange or by asset. You do need to have records of each individual disposal in case HMRC asks, but the form only requires the totals.
My gain is from Bitcoin, Ethereum, and several altcoins. Does each get a separate box?
No. All cryptoassets are pooled together for SA108 purposes. Total gains from all disposals go in box 3; total losses from all disposals go in box 4. There is no breakdown by asset type on the form.
I made gains but also received staking rewards. Which forms do I need?
You need both SA100 (for the staking income, reported under other income) and SA108 (for the capital gains from disposals). The two are reported separately and taxed at different rates — income tax on staking, CGT on disposals.
What if I made an error on a previous year's SA108?
You can amend a Self Assessment return online up to 12 months after the filing deadline. For corrections older than that, you need to write to HMRC. If you underpaid tax, you will need to pay the outstanding amount plus interest. Acting proactively is always better than waiting for HMRC to discover an error.
General information only. Check HMRC's current guidance and consult a qualified adviser if unsure.