How to Keep CGT Records — What HMRC Expects and for How Long

HMRC can ask you to prove any number on your tax return. If you can’t, they’ll estimate the figure themselves — and their estimate won’t be in your favour. Record keeping is boring. It’s also the difference between a smooth filing process and a stressful enquiry.

What records to keep

For every share or fund transaction, HMRC expects you to retain:

Buy trades: Date, number of shares, price per share, total cost, broker commission, stamp duty (0.5% on UK shares), and the exchange rate used if the trade was in foreign currency.

Sell trades: Date, number of shares, price per share, total proceeds, broker commission, and the exchange rate.

Corporate actions: Stock splits, bonus issues, rights issues, mergers, demergers — dates and details of how your holding changed. See our stock splits guide for how these affect your pool.

Your CGT calculation: Which matching rule applied to each disposal, the cost basis used, the gain or loss. This is your audit trail. HMRC’s record-keeping guidance specifically requires you to keep “records of how you’ve worked out each gain or loss.”

Exchange rates: If you trade US stocks, keep a record of the HMRC monthly exchange rate used for each conversion.

How long to keep them

The statutory minimum is at least 5 years and 10 months after the end of the tax year. In practice, HMRC rounds this to “at least 5 years after the 31 January filing deadline” — which works out to the same thing.

For 2025/26 (filing deadline 31 January 2027): keep records until at least 31 January 2032.

But there’s an important caveat: if you still hold shares you bought years ago, you need the original purchase records to calculate your gain when you eventually sell. Keep buy records for as long as you hold the investment, plus at least 5 years after you sell.

The gov.uk guidance on keeping records puts it clearly: “You must keep your records for at least 5 years after the 31 January submission deadline of the relevant tax year.”

What happens if you lose your records?

Two scenarios, neither good:

If HMRC opens an enquiry and you can’t provide records: They can issue a “determination” — their own estimate of what you owe. Under TMA 1970, they have powers to assess tax based on the information available, which typically means assuming higher gains and lower costs than the reality.

If you’re filing and don’t have records: You’ll need to reconstruct your cost basis from whatever evidence you can find — broker statements, bank transactions, old emails. It’s painful and error-prone. Some brokers will provide historical statements on request, but not all retain data beyond 3-7 years.

Broker CSV exports are your best friend

Download and save your broker’s transaction history every year. Do it now while you’re thinking about it. Brokers don’t keep records forever, and if they close down (see our guide on multiple broker calculations), the data goes with them.

Save the CSV files on your computer with a clear naming convention: robinhood-uk-2025-26.csv, trading212-gia-2025-26.csv. Back them up to cloud storage.

TaxBull’s session save feature lets you download your entire calculation state as a JSON file — transactions, exchange rates, stock splits, ERI entries, and results. This is a complete audit trail you can reload years later if HMRC ever asks questions.

Contract notes

The confirmation you receive from your broker after each trade (called a “contract note”) is your primary evidence of a transaction. Most brokers send these by email or make them available in their app. Save them. If there’s ever a discrepancy between your CSV export and reality, the contract note is the authoritative record.

Practical system

At the end of each tax year (after 5 April):

1. Download full transaction history CSVs from every broker you used.

2. Run your CGT calculation (manually or via TaxBull).

3. Save the calculation output / session file.

4. File your SA108 by 31 January.

5. Archive everything in a folder named by tax year.

Ten minutes of housekeeping per year. Worth every second.

This is general information only. HMRC’s record-keeping requirements may change. Check gov.uk for the latest guidance.