Crypto Records HMRC Requires: What to Keep, How Long, and How to Rebuild Your History When an Exchange Has Closed

HMRC does not ask for your crypto records when you file. It asks for them later — in an enquiry, after a nudge letter, or when a figure on your return does not match what an exchange has reported under CARF. By then the exchange may have closed, the CSV export may have been switched off, and the person who could have explained a 2021 transaction is you, four years on. This guide covers what you are required to keep, for how long, and how to rebuild a history that has gaps.

What HMRC says you must keep: CRYPTO10400

The Cryptoassets Manual at CRYPTO10400 lists the records HMRC expects an individual to hold for each transaction:

• the type of cryptoasset,
• the date of the transaction,
• whether it was a purchase, sale, swap, gift, receipt of income or transfer,
• the number of units,
• the value in pounds sterling at the date of the transaction,
• the cumulative total of units held,
• bank statements and wallet addresses.

The manual also notes that exchanges may not keep records for long and that the onus is on you. That is not a throwaway line; it is HMRC's answer in advance to "the exchange closed so I don't have the data".

How long to keep them

The retention rules are in TMA 1970 s.12B. For a Self Assessment return that is not for a business, records must be kept until the later of 22 months after the end of the tax year or the end of any enquiry. For someone with trading income (which HMRC could argue includes very active crypto dealing) it is five years after 31 January following the tax year.

Those are minimums for the return itself. The practical retention period for crypto is longer, for two reasons:

1. Section 104 pools carry forward. The cost of a token you sell in 2027 was set by purchases in 2020. If HMRC questions the 2027 disposal, the 2020 purchase record is what supports it. You need acquisition records for as long as you hold any of the pool.
2. Assessment time limits. HMRC can go back four years for an ordinary error, six for carelessness and twenty for deliberate under-declaration (TMA 1970 ss.34 and 36). The investigation time limits guide covers this. Records are your defence against the "careless" label that doubles the window.

A sensible rule: keep everything, permanently, in at least two places.

What "the value in sterling" means in practice

Each transaction needs a sterling value at the date. For a purchase with pounds on a UK exchange it is on the confirmation. For a swap on a DEX in April 2022 it is the token's price on that day, converted from USD at that day's exchange rate, and you need to be able to show where the price came from. HMRC does not prescribe a source but expects consistency (CG78300 onwards for foreign currency generally). Record the source alongside the figure.

Rebuilding a history: the method

When an exchange has closed or an account is gone, work through these sources in order.

1. The blockchain

Anything that touched a wallet you control is on-chain permanently. Deposits to and withdrawals from the closed exchange appear as transfers to and from its addresses. That gives you dates and quantities for everything that entered or left the exchange, which bounds what could have happened inside it. A block explorer export, or a wallet-address scan, rebuilds this in minutes; cryptolens.uk's scanner reads a public address across 29 chains and prices each transfer in sterling on the day, which is the tedious part when done by hand.

What the chain cannot show is trading inside the exchange's own books. For that you need the next sources.

2. Bank and card statements

Every pound in and out of an exchange went through a bank. Statements give you the fiat side: how much you deposited, when, and how much came back. Combined with the on-chain deposits and withdrawals, this fixes the total cost of everything you ever bought there and the total proceeds of everything you sold to pounds. If the exchange is gone, that is often enough to reconstruct the pool cost in aggregate even if individual trades are lost.

3. Email

Exchanges send confirmations. Search for the exchange's domain and export every message — trade confirmations, deposit notices, withdrawal notices, monthly statements. Coinbase, Kraken and Binance all send order confirmations. Even a closed exchange's emails survive in your inbox.

4. Claims portals and administrators

FTX creditors received a schedule of their account balance as at the bankruptcy date through the claims process; Celsius likewise; Mt Gox trustees issued balance statements. Those documents establish what you held on a specific date and are admissible as evidence of your position. They do not give you cost basis, but combined with the fiat and on-chain records they fix the quantity.

5. Old tax software exports, screenshots, spreadsheets

If you ever synced the exchange to a tracker, that tracker's export may still exist even though the exchange does not. A Koinly or CoinTracker CSV from 2022 is an acceptable record; cryptolens.uk imports Koinly's format directly for this reason.

6. Reasonable estimation, disclosed

Where a specific trade genuinely cannot be reconstructed, HMRC accepts a reasonable estimate if you say that it is one. Put the method in the notes box on the return: "Cost basis for X estimated from bank deposits and withdrawal quantities; exchange closed in 2022 and export unavailable." An estimate that is disclosed is a reasonable-care position. An estimate presented as a fact is the opposite.

Worked example: a closed exchange

Dan used an exchange from 2020 to 2022 that no longer exists. He has no export. He has bank statements showing £8,400 deposited in total and £2,100 withdrawn to his bank, on-chain records of 0.9 BTC withdrawn from the exchange's address to his own wallet in 2021, and emails confirming three of the buys.

Reconstruction: total fiat cost £8,400, of which £2,100 came back as pounds. The 0.9 BTC withdrawn is what remains. Dan can show that the £2,100 of sales and the 0.9 BTC together consumed £8,400 of cost. Allocating cost between the sold portion and the withdrawn BTC needs the individual trade dates — the three emails cover most of it and the remainder is estimated in proportion to the deposits at the time. His 2021/22 return reports the sales; his ongoing pool holds 0.9 BTC at the reconstructed cost, with the method noted. It is not perfect. It is defensible, and it is far better than the £0 cost basis HMRC would apply if no cost could be evidenced at all.

Assets lost with the exchange

If the exchange collapsed and your tokens went with it, the tax question is separate from the records question. A claim against an administrator is an asset; if it becomes worthless a negligible value claim under TCGA 1992 s.24 may be available. Losses from theft are generally not allowable because there is no disposal. The lost and stolen crypto guide covers both routes.

Set it up so this never happens again

• Export every exchange's full history at the end of each tax year, on 6 April, before you need it.
• Save the export in two places, one of them not on the same laptop.
• Keep a one-line note per unusual transaction while you still remember what it was.
• Where possible, withdraw to a wallet you control; the chain is the only record that cannot be turned off.

This is general information, not personal tax advice.