The SA108 is the Capital Gains Summary part of your Self Assessment return. Crypto has its own section on it from 2024/25. This page covers who has to fill it in, which box each figure goes in, and the matching rules that decide those figures.
You need the capital gains pages when any one of these is true for the tax year (6 April to 5 April):
A disposal is selling for pounds, swapping one token for another, spending crypto and gifting it to anyone other than your spouse. Staking, mining and similar rewards are income, and income goes on the main return instead.
The 2025/26 SA108 puts cryptoassets on page CG2; the previous year used the same page but included box 18 for attributed gains. Before 2024/25, crypto went in the general “other property, assets and gains” section.
| 2025/26 · SA108 2026 (CG2) | 2024/25 · SA108 2025 (CG2) | Box |
|---|---|---|
| 14 | 14 | Number of disposals |
| 15 | 15 | Disposal proceeds |
| 16 | 16 | Allowable costs (including purchase price) |
| 17 | 17 | Gains in the year, before losses |
| — | 18 | Attributed gains where personal losses cannot be set off |
| 19 | 19 | Losses in the year |
| 20 | 20 | If you're making any claim or election, put the relevant code in the box |
| 21 | 21 | Total gains or losses on the disposal of an asset of this type reported on Real Time Transaction returns |
| 22 | 22 | Tax on gains in box 21 already paid |
Box 20 is a claim code; use it only if you are making a claim or election. Boxes 21 and 22 apply only if you reported crypto disposals through HMRC’s Real Time Transaction service.
| Losses and adjustments | Box |
|---|---|
| 45 | Losses brought forward and used in-year |
| 46 | Income losses of the year set against gains |
| 47 | Losses available to be carried forward |
| 48 | Losses used against an earlier year's gain |
HMRC’s SA108 notes also ask you to enclose your computations, with the details of each gain or loss, as well as filling in the boxes. GOV.UK: SA108 and notes.
Each disposal is matched first with tokens of the same kind bought on the same day. What is left is matched with tokens bought in the following 30 days. Only then does it come out of the Section 104 pool, which holds everything else at its average cost. HMRC CRYPTO22200.
| Pool | 4 ETH bought for £6,000 in total, so £1,500 each |
| 10 June | Sell 2 ETH for £5,000 (£2,500 each) |
| 20 June | Buy 1 ETH back for £2,200 |
| 30-day match | 1 ETH: £2,500 − £2,200 = £300 gain |
| Pool match | 1 ETH: £2,500 − £1,500 = £1,000 gain |
| Result | Gain £1,300. The pool is left with 3 ETH at £4,500 |
On the 2025/26 SA108 that is box 14: 1 disposal, 15: £5,000, 16: £3,700 (£2,200 + £1,500) and 17: £1,300. Without the 30-day rule the whole sale would come from the pool at £3,000 and the gain would be £2,000.
Import your exchanges and wallets and Moonscape applies the matching rules above to every disposal. Three documents come out. See a filled-in SA108 report or open the full UK sample pack.
Every box above with the figure to enter, in the right layout for the year, plus the losses boxes 45 to 48 and how box 47 was reached.
Each disposal with its same-day, 30-day or Section 104 match, the pool history per token, and allowable costs. HMRC asks you to enclose this with the return.
Staking, mining, airdrops treated as income and other rewards, in pounds at the time you received them. These go on the main return, not the SA108.
You need the capital gains pages if your gains after losses are above the annual exempt amount (£3,000 for 2024/25 and 2025/26), if your total disposal proceeds are above £50,000 (from 2023/24), or if you want to claim a loss. Selling for pounds, swapping one token for another, spending crypto and gifting it to anyone other than a spouse are all disposals.
For 2025/26, the SA108 2026 has cryptoassets on page CG2 in boxes 14 to 17 and 19 to 22; box 18 is not in use. The 2024/25 form also used boxes 14 to 22, with box 18 for attributed gains where personal losses cannot be set off. Earlier years used the general other property, assets and gains section. Losses carried in or out use boxes 45 to 48.
For cryptoassets you have to. HMRC matches each disposal first with tokens bought the same day, then with tokens bought in the next 30 days, and only then with the Section 104 pool at its average cost. FIFO and other methods are not options for a UK return.
Enter a crypto capital loss in box 19. A capital loss has to be claimed within 4 years of the end of the tax year it arose in, and it then carries forward with no time limit. Losses from the same year are set against gains first; losses brought forward only bring your gains down to the annual exempt amount, so the allowance is never wasted.
£35 to £159 per tax year, set by that year’s transactions. Buy the year first and import afterwards, or import free and pay when you see your count. Got a letter from HMRC? Start with what to do about an HMRC warning letter.