Records and evidence HMRC may ask for

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What to keep for a capital loss

GOV.UK lists the records to keep for Capital Gains Tax — and the same documents prove a loss. Keep receipts, bills and invoices showing the date and amount:

• you paid for the asset;
• of additional costs — such as fees for professional advice, Stamp Duty, improvement costs, or the cost of establishing market value;
• you received for the asset — including later instalments, or compensation if it was damaged.

Also keep contracts for buying and selling (for example from solicitors or stockbrokers) and copies of any valuations. For worthless shares, keep the evidence you used to support a negligible value claim, such as letters from a liquidator.

Cryptoassets

GOV.UK says that for each pool of tokens you must keep separate records for each transaction: the type of tokens, the date you disposed of them, the number disposed of and the number left, the value in pounds sterling, bank statements, and the pooled costs before and after. Exchange reports can help, but GOV.UK warns they aren’t tax calculations and won’t track your pooled costs. See cryptoasset losses.

Business losses

Keep the records that support your accounts: sales and income, purchases and expenses, and the calculations behind capital allowances. The loss figure on your return should be traceable back to them.

How long to keep records

GOV.UK’s example: if you sent your 2022 to 2023 return online by 31 January 2024 as a self-employed person, keep your records until at least the end of January 2029. The law (section 12B of the Taxes Management Act 1970) extends these periods while an enquiry is open, and there can be a penalty of up to £3,000 for failing to keep records.

Lost records

GOV.UK says you must try to recreate records you can’t replace. If you use estimated or provisional figures, say so in the "Any other information" box on your return.

What HMRC can ask for

HMRC’s factsheet CC/FS1a explains that a compliance check is to make sure you’re paying the right tax and getting the right allowances and reliefs. HMRC may ask you to send information or documents, to meet, or — for a business — to inspect premises, assets and records. For claims made outside a return, the law lets HMRC ask for accounts, statements and documents reasonably needed, and a repayment claim needs documentary proof that the tax was paid.

If you get a compliance check letter and need help, see where to get help.

Questions people ask

How long should I keep records that support a loss?

GOV.UK says at least 22 months after the end of the tax year if you’re not self-employed and filed on time, and at least 5 years after the 31 January deadline if you are self-employed. If you’re carrying a loss forward, it’s sensible to keep the evidence until the loss is used up and the returns using it can no longer be checked.

Sources

Checked 4 October 2026 for the 2026/27 tax year. We read these primary sources for this guide:

1. GOV.UK: Capital Gains Tax — Record keeping (gov.uk)
2. GOV.UK: Keeping your pay and tax records — How long to keep your records (gov.uk)
3. GOV.UK: Business records if you’re self-employed — How long to keep your records (gov.uk)
4. Taxes Management Act 1970, section 12B (legislation.gov.uk)
5. HMRC Self Assessment Claims Manual SACM4015: Records for claims outside a return (gov.uk)
6. GOV.UK: Check if you need to pay tax when you sell cryptoassets (gov.uk)
7. HMRC factsheet CC/FS1a: About compliance checks (gov.uk)
8. Taxes Management Act 1970, Schedule 1A (legislation.gov.uk)

Contains public sector information licensed under the Open Government Licence v3.0. This guide adapts and summarises that information in our own words. taxloss.co.uk is an independent guide. It is not affiliated with, endorsed by or connected to HM Revenue & Customs (HMRC) or the UK Government. Spotted something out of date? Tell us.

More on returns, deadlines & records

• 19Deadlines for loss claimsEvery loss relief has a time limit, and they aren’t all the same. Some run 4 years from the end of the tax year; some only to the first anniversary of the 31 January filing date. Here are the main ones in one place, with the 2026/27 dates.
• 20Where losses go on your Self Assessment returnA plain-English map of the loss boxes on the Self Assessment supplementary pages — capital gains (SA108), self-employment (SA103), partnership (SA104), UK property (SA105) and additional information (SA101). Box numbers are from the 2025–26 forms.
• 21Amending a return or claiming laterForgot to claim a loss? You can usually amend your Self Assessment return within 12 months of the 31 January deadline. After that, many loss claims can still be made by letter within their own time limits — and overpayment relief is available for up to 4 years.
• 22Making Tax Digital for Income Tax from April 2026Since 6 April 2026, sole traders and landlords with qualifying income over £50,000 must keep digital records, send quarterly updates and file their tax return through compatible software. Here’s who is affected, when, and what GOV.UK says about losses.
• 24When to get professional helpMany losses are simple enough to claim yourself. Some aren’t — large or complex losses, businesses stopping, partnerships and companies, overseas issues or an HMRC check. Here’s who can help, and how to choose.