The SA108 is the Capital Gains Tax summary supplementary page to the SA100 tax return. It reports the year's disposals of assets by category, the gains and losses on them, the losses and reliefs claimed and the Capital Gains Tax due, and a computation of each gain must be attached.
Who completes it
Anyone who in the tax year sold or gave away chargeable assets with total proceeds of more than £50,000, made total chargeable gains above the £3,000 annual exempt amount, wants to claim a loss or a relief, or has non-resident Capital Gains Tax to report. Someone who sold UK residential property will usually have already filed a 60-day property return and paid the tax, which is then credited here.
What it asks for
- A section for each kind of asset: residential property, other property and assets, listed shares and securities, unlisted shares and securities and crypto-assets, each with the number of disposals, the proceeds, the allowable costs, the gains and the losses.
- Losses and adjustments: losses brought forward and set against the year’s gains, losses to carry forward, and claims to reliefs such as Business Asset Disposal Relief.
- Tax already paid on UK property returns and real-time transactions.
- A computation for each gain, attached to the return or summarised in the Any other information box.
For 2025-26 the gains above the annual exempt amount are taxed at 18% within any unused basic-rate band and 24% above it, and gains that qualify for Business Asset Disposal Relief or Investors’ Relief at 14% (18% for disposals from 6 April 2026). Capital Gains Tax is paid with the balancing payment on 31 January and is never part of the payments on account.
In Tax Optimiser
Add the Capital Gains (SA108) section and enter the totals for each asset category as on the paper form. The calculation applies in-year and brought-forward losses and the annual exempt amount, taxes what remains at the right rates and credits tax already paid on property returns up to the amount due. HMRC will not accept the page without a summary of the computation, so put a line per disposal in the Additional Information box (box 54); the pre-flight checks flag it until it is there.
Read more: the Self Assessment supplementary pages.
