The SA108 capital gains summary pages report the year’s disposals as totals by asset type, with a computation for each gain or loss attached. Gains already reported on a 60 day UK property return go in box 9, the tax due on those returns goes in box 10, and the amount paid is treated as a payment on account, so it reduces the 31 January balancing payment or is repaid if it was too much. The 2026 version of the form covers the 2025 to 2026 tax year.

Who has to fill in the SA108?

The HMRC notes for the 2025 to 2026 pages say you must complete them if any of these apply:

  • you disposed of chargeable assets worth more than £50,000;
  • your chargeable gains before losses were more than the £3,000 annual exempt amount;
  • you have gains from an earlier year taxable in this year;
  • you want to claim an allowable loss or make a capital gains claim or election;
  • you previously used the remittance basis and remitted earlier foreign gains, or you are claiming under the foreign income and gains (FIG) regime or the temporary repatriation facility;
  • you disposed of an interest in UK property while non resident, or in the overseas part of a split year.

You do not need the pages if you only disposed of private cars, personal possessions worth up to £6,000 each, shares in ISAs or PEPs, gilts (including National Savings Certificates and Premium Bonds), or a main home fully covered by private residence relief. See which assets are exempt.

How is the form laid out?

Section Boxes What goes there
Residential property and carried interest 3 to 13C Residential property disposals, including those already reported on 60 day or real time returns
Cryptoassets 13.1 to 13.8 Disposals of cryptoassets
Other property, assets and gains 14 to 22 Everything not covered elsewhere, and all gains where Business Asset Disposal Relief is claimed
Listed shares and securities 23 to 30 Quoted shares, UK OEICs and authorised unit trusts
Unlisted shares and securities 31 to 44 Unlisted and AIM shares, EIS and SEIS shares, share loss relief claims
Losses and adjustments 45 to 48 Losses brought forward, used and carried forward
Reliefs and tax adjustments 49 to 52 Investors’ Relief, Business Asset Disposal Relief, adjustments
Non resident capital gains 52.1 to 52.5 Gains on UK property chargeable as non resident gains
Any other information 53 and 54 Estimates, valuations, return references and explanations

In each asset section you give the number of disposals, total proceeds, total allowable costs, total gains before losses, and total losses. The notes say gains are entered after any reliefs that reduce them, but not after the annual exempt amount, which HMRC deducts automatically.

What computations must you attach?

The SA108 itself says you must enclose your computations, including details of each gain or loss, as well as filling in the boxes. The notes ask for computations, valuations, specified claim forms and any working sheets, and say you must not cross through boxes or write “see attached” in them.

For a simple disposal, the working sheet on page CGN 15 of the notes runs from proceeds, less incidental costs of sale, less cost or 31 March 1982 value, acquisition costs and improvement costs, to a net gain after reliefs. The notes say you cannot use it where you acquired the asset by exercising an option, where the disposal is a part disposal, or where gains must be aggregated for a Business Asset Disposal Relief claim. Costs that can be deducted are explained in allowable costs.

A good computation also states the asset, dates of acquisition and disposal, any market value used and its basis, and any relief claimed. If any figure is an estimate or valuation, the notes say to put X in box 53 and explain in box 54 or the computation where and why you estimated, how you worked it out, and the valuation date and asset description. See estimated figures on a tax return.

How are claims and elections shown?

Claims are shown with a three letter code in box 8, 13.6, 20, 28 or 36, with details in box 54. The codes are PRR (private residence relief without letting relief), LET (with letting relief), GHO (gift holdover relief), ROR (rollover relief), PRO (provisional rollover relief), ESH (employee shares), BAD (Business Asset Disposal Relief), INV (Investors’ Relief), NVC (negligible value claims), EOT (Employee Ownership Trust), OTH for other claims and MUL where more than one applies.

How are 60 day return payments credited?

A UK resident who has already filed a Capital Gains Tax on UK property return still reports the disposal on the SA108. The notes say:

  • Box 9: the overall gain or loss on UK residential property reported on those returns, combining gains and losses if there was more than one disposal, with a minus sign for a net loss.
  • Boxes 6 and 7: the individual gains and losses must also be included in these totals.
  • Box 10: the total tax you were required to pay on those returns.
  • Box 54: the reference number of each UK property return.

Where all of a gain on a UK property return qualifies for Business Asset Disposal Relief, the notes say it goes in box 17 and box 21, with the tax in box 22, rather than boxes 9 and 10. Disposals reported through the real time service follow the same pattern, using boxes 11 and 12, 13.7 and 13.8, 21 and 22, 29 and 30, or 37 and 38.

The legal basis for the credit is section 59B(1) of the Taxes Management Act 1970. The balancing payment is the difference between the tax in your self assessment and the payments on account you have made, which expressly includes payments under Schedule 2 to the Finance Act 2019, the 60 day regime. That difference is payable or repayable by 31 January following the tax year.

Worked example: a property sale and a later loss

Illustration only. Dana sold a let flat in June 2025 and she is a higher rate taxpayer, so her 60 day return showed a £40,000 gain and £8,880 of tax (24% of the £37,000 left after the annual exempt amount), which she paid. In February 2026 she sold shares at a £10,000 loss. On her 2025 to 2026 SA108:

Box Entry
3 to 6 1 disposal, its proceeds and costs, gain £40,000
9 £40,000
10 £8,880
23 to 27 The share sale, with the £10,000 loss in box 27
54 The UK property return reference

Her self assessment now taxes £27,000 (£40,000 less the £10,000 loss and the £3,000 annual exempt amount) instead of £37,000, so her final capital gains tax is lower than the £8,880 already paid. The excess is set against the rest of her 2025 to 2026 liability or repaid under section 59B. The share loss could not reduce the 60 day payment because it was made after the flat sale; see 60 day returns.

How are losses entered?

Losses of the year go in the relevant section (boxes 7, 13.5, 19, 27 or 35). Box 45 is for losses brought forward and used, and the notes say these can only reduce gains down to the annual exempt amount, which for 2025 to 2026 is £3,000 for individuals and £1,500 for most trustees. Box 47 shows losses carried forward, including clogged losses on disposals to connected persons, which can only be used against gains on disposals to the same person. See claiming capital losses.

Foreign gains on which you claim foreign tax credit relief go on the SA108 as well as in box 33 of the SA106 foreign pages.

When is the SA108 due?

It is part of the main return. GOV.UK says the 2025 to 2026 return is due by 31 October 2026 on paper or 31 January 2027 online, with any tax owed paid by 31 January 2027. If a sale was made under an unconditional contract that had not completed when you file, the notes say to give details in box 54 and provide the computation once it completes.

What are the common mistakes?

  • Entering a gain in box 9 but leaving it out of the box 6 total.
  • Deducting the annual exempt amount yourself.
  • Omitting the 60 day return or real time references from box 54.
  • Using brought forward losses to reduce gains below £3,000.
  • Assuming that because tax was paid within 60 days, the disposal does not need to go on the return.

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Sources

Reviewed by Christine Anderson, Broker, Solar Protect. Last reviewed 19 October 2026. Part of Accountapedia, the Solar Protect guide to UK tax and accounting. This page is general information, not personalised advice.