The three reasons you may need to report
- Your gains are over the £3,000 allowance. If you're in Self Assessment, fill in the capital gains pages (SA108) when your gains before losses are more than £3,000. If you're not, you need to tell HMRC when you have tax to pay (gov.uk).
- You sold more than £50,000. If you're registered for Self Assessment, you report your gains on your return when the total you sold assets for in the tax year was more than £50,000, even with no tax to pay. It's the sale value that counts, not the profit.
- You want to use a loss. Reporting is optional, but a loss you never report can't be set against later gains. Claim within 4 years of the end of the tax year (gov.uk).
How to report if you're not in Self Assessment
UK residents can use HMRC's real time Capital Gains Tax service. For sales in 2025/26, report by 31 December 2026 and pay by 31 January 2027. Or register for Self Assessment and report on a return.
Why your broker's profit figure may not be the answer
HMRC works out each gain using the same-day rule, the 30-day rule and your Section 104 pool, in pounds. Most broker statements use a different method or another currency, so the profit they show can be some way off, and close to £3,000 that decides whether you report. Upload your broker export and FiscalFox works out the HMRC figures for free.
What this check doesn't cover
It uses only the figures you enter. Losses from earlier years, reliefs, selling a home or other property, gifts, being non-resident and trusts can all change the answer. It isn't tax advice.
Frequently asked questions
Do I need to report capital gains if I have no tax to pay?
Sometimes. If you are registered for Self Assessment, you must report your gains on your tax return when the total you sold assets for in the tax year was more than £50,000, even if no tax is due. You also fill in the capital gains pages when your gains before losses are more than the £3,000 allowance, or when you want to claim a loss.
What counts towards the £50,000?
The total sale proceeds of the assets you sold in the tax year, not your profit. Sales inside an ISA or a pension do not count, because they are not subject to capital gains tax.
I am not registered for Self Assessment. How do I report?
If you have capital gains tax to pay on shares or other assets, you can use HMRC's real time Capital Gains Tax service if you are a UK resident. For gains made in 2025/26, report by 31 December 2026 and pay by 31 January 2027. You can also register for Self Assessment and report on a tax return instead.
Should I report a loss?
You do not have to, but a loss you never report cannot be used. Reporting it lets you set it against gains in later years. You must claim within 4 years of the end of the tax year you made the loss.
Is this check tax advice?
No. It applies HMRC's published reporting rules to the figures you type in. It does not know about losses from earlier years, reliefs, residence or property sales, which can change the answer.
Official UK tax references
This guide is checked against published GOV.UK and HMRC material. FiscalFox is a calculation tool, not personal tax advice; review unusual transactions with a qualified adviser.