SA108 capital gains summary: reporting gains on your return

Who needs it

• Anyone whose total gains for the tax year are above the £3,000 annual exempt amount.
• Anyone who already files a Self Assessment return and needs to report a disposal, as an alternative to HMRC's real-time Capital Gains Tax service.
• People claiming reliefs or reporting losses, such as Private Residence Relief or Business Asset Disposal Relief.
• Non-UK residents selling UK property or land: HMRC says they must report every sale, even when no tax is due.

What you need before you start

• For each disposal: what you sold or gave away, the dates you acquired and disposed of it, and the amounts you paid and received.
• Allowable costs, such as fees for buying and selling and the cost of improvements.
• Your share pool records if you sold shares in a company you've bought into more than once.
• Details of any relief you're claiming, and losses from earlier years.

How to file SA108

1. 1Add up your gains for the tax year and compare them with the annual exempt amount.
2. 2For UK residential property, report and pay within 60 days of completion. Don't wait until the next tax year.
3. 3For other gains, use the real-time Capital Gains Tax service if you're eligible and report by 31 December after the tax year, or put them on your Self Assessment return.
4. 4On the return, complete the capital gains section online, or the SA108 PDF with your paper SA100, using HMRC's notes and the relevant helpsheet.

When you need SA108

HMRC's first test is whether your total gains for the tax year are above your tax-free allowance, the annual exempt amount. If they are, you need to report and pay. Gains other than UK residential property are reported in the tax year after the sale, either on a Self Assessment return or, if you're eligible, through the real-time Capital Gains Tax service by 31 December.

The SA108 itself is four pages with fifteen pages of notes, and HMRC lists more than twenty helpsheets beside it. The ones most people need are HS283 (Private Residence Relief), HS284 (shares) and HS275 (Business Asset Disposal Relief).

The 60-day rule for UK property

For UK residential property completed on or after 27 October 2021, the gain has to be reported within 60 days of completion. HMRC is clear that you shouldn't wait until the next tax year, or you may have to pay interest and a penalty.

If you're not UK resident, you must report every sale of UK property or land, even if no tax is due.

Common mistakes

• Waiting for the tax return to report a UK residential property sale. HMRC warns that doing so can bring interest and a penalty.
• Forgetting that non-residents must report every UK property or land sale, even with no tax to pay.
• Leaving out allowable costs such as buying and selling fees, which reduce the gain.
• Reporting shares sale by sale without the share pooling rules. HMRC's helpsheet HS284 sets out how shares are matched.