How to Report Capital Gains on Shares (SA108)

For shares, you need to fill in the capital gains pages (called SA108) of a Self Assessment tax return if any of these apply for the tax year:

• You sold chargeable assets, such as shares held outside an ISA or pension, for more than £50,000 in total, even if you made no gain.
• Your gains, before taking off any losses, were more than the £3,000 tax-free allowance.
• You want to claim a loss, so you can use it against gains now or in the future.

The second point catches people out. You can owe no tax because your losses bring your total below £3,000, but you still have to report if your gains on their own were more than £3,000. The worked example below shows this.

• A Self Assessment tax return, using the SA108 capital gains pages. If you've never sent a tax return, you need to register with HMRC by 5 October after the end of the tax year.
• HMRC's online "report and pay your Capital Gains Tax" service. Any UK resident can use it, and it's handy if you don't otherwise fill in a tax return. Report by 31 December after the tax year ends and pay by 31 January. You'll need to include a copy of your calculations.

If you're already in Self Assessment and use the online service, you still need to include the sales on your tax return as well (see boxes 29 and 30 below).

For every sale in the tax year, you need:

• the date, the company or fund, and the number of shares sold
• how much you sold them for, and the selling fees
• what those shares cost you, using HMRC's matching rules: same day, then the next 30 days, then the Section 104 average cost
• the gain or loss on the sale

Our calculator works these out for you. Paste in your trades and open "How the tax is calculated" to see the proceeds, fees, cost and gain or loss for each sale in the tax year.

Shares in listed companies, most ETFs and investment trusts, UK open-ended investment companies (OEICs) and authorised unit trusts go in the "Listed shares and securities" section. On the form for the 2025–26 tax year, that's boxes 23 to 30:

Two boxes in the "Losses and adjustments" section may also apply:

• Box 45: Losses brought forward and used in-year. Losses from earlier years that you're using now. You can only use them to bring your gains down to the £3,000 allowance, not below it.
• Box 47: Losses available to be carried forward. Losses you haven't used yet and want to keep for later years.

Private company shares go in the "Unlisted shares and securities" section instead. Box numbers can change from year to year, so check the notes for the year you're filing. HMRC's online return asks for the same figures, though it may not show the box numbers.

During the 2025–26 tax year, you made three sales. The costs below already include buying fees and use HMRC's matching rules.

HMRC asks you to send your calculations (it calls them "computations") with the capital gains pages. They should show each sale: the date, what you sold, the proceeds, the costs and the gain or loss. Fill in every box that applies. Don't write "see attached" in the boxes instead of a figure.

If any of your figures are estimates, put an X in box 53. Box 54 is for any other information, including reference numbers if you used the online Capital Gains Tax service.