HMRC can demand records going back years — and most crypto investors are not keeping nearly enough of them. Poor record-keeping is the single biggest reason that crypto tax returns contain errors, and it is the thing most likely to make an HMRC enquiry painful rather than routine.
Why crypto record-keeping is harder than it looks
For shares in an ISA, your broker does the record-keeping. For crypto, you are responsible for assembling records across multiple exchanges, multiple wallets, DeFi protocols, and years of history — often in different currencies, different formats, and different levels of completeness. Exchanges have closed without warning, deleted old data, or restricted exports. The sooner you establish consistent habits, the less painful this becomes.
Ten habits that make a real difference
Export your transaction history at least once a year
Do not rely on exchanges retaining your complete history indefinitely. Several major exchanges have closed, restricted access, or deleted historical exports without warning. Download a full CSV export from every exchange you use at the end of each tax year (5 April) and store it somewhere permanent.
Record GBP values at the time of each transaction, not today
HMRC requires GBP values at the date of each transaction — not retrospective valuations. If you bought ETH for USDT on a non-GBP exchange, you need the USDT/GBP rate at that specific date and time. Historical exchange rate data becomes harder to find the longer you wait, and some data providers only retain it for a limited period.
Label every transaction type clearly
Was it a trade, a transfer between your own wallets, a payment for goods, a gift, staking income, or a fee? The tax treatment differs significantly between these categories. A transfer between your own wallets is not a taxable event; a gift to a friend is. Labelling at the time takes seconds; untangling ambiguous transactions months later takes hours.
Record every fee paid on every transaction
Exchange fees and gas fees are allowable costs that reduce your gain or increase your cost basis. Many investors forget to record fees, particularly small gas fees, and end up paying more tax than necessary. For active on-chain users, cumulative gas fees across a year can represent a meaningful reduction in taxable gain.
Maintain a list of all your wallet addresses
When HMRC asks about a particular on-chain transaction, you need to demonstrate which wallets belong to you. A simple spreadsheet listing each wallet address, the blockchain, and when you started using it takes minutes to create and can save significant trouble in an enquiry. This is also essential for correctly identifying personal transfers versus disposals.
Document any lost or stolen assets immediately
If you lose crypto — to a scam, an exchange insolvency, or a lost seed phrase — document it thoroughly at the time: screenshots, correspondence, blockchain evidence, reports to authorities. Evidence obtained immediately is far more credible than reconstructed evidence from memory months later. This documentation may support a capital loss claim.
Record DeFi positions at entry and exit
DeFi protocols rarely produce useful tax exports. For every liquidity pool deposit, staking position, or lending protocol interaction: record what you deposited, when, the GBP value at entry, what you received in LP or receipt tokens, and what you received on exit. This is the foundation for any DeFi tax calculation and is almost impossible to reconstruct from memory.
Keep supporting evidence for unusual transactions
For gifts, airdrops, compensation payments, inheritance, hard fork tokens, and other non-standard events: save the relevant emails, app confirmations, blockchain transaction hashes, or announcements from the project. These provide the documentary evidence that a transaction was what you say it was, rather than a disposal you are trying to characterise differently.
Reconcile your records monthly rather than at year-end
One hour per month spent reviewing your transactions and confirming your records are complete is far less painful than three days of frantic record recovery in January. Monthly reconciliation also catches discrepancies — missing transactions, incorrectly labelled events — when they are fresh and fixable, rather than months later when they are ambiguous.
Use a tool that maintains a persistent audit trail
Spreadsheets are fragile, prone to formula errors, and difficult to audit. A dedicated crypto tax tool like Polyconomic imports your full history, maintains your Section 104 pool continuously, flags matching events, and preserves a complete audit trail that shows exactly how every gain was calculated. Your records are always current, not just at year-end.
HMRC can request records going back up to 20 years in cases of deliberate underreporting. Even for straightforward mistakes, they can go back 6 years. For assets still held in your Section 104 pool, records may be relevant for as long as you hold that asset — potentially decades.
Frequently asked questions
What format does HMRC require records to be kept in?
HMRC does not prescribe a specific format. Records can be kept in spreadsheets, accounting software, or dedicated crypto tax tools. What matters is that the records are complete, accurate, and available on request. HMRC will typically ask for transaction-level detail showing dates, quantities, GBP values, and the nature of each event.
My exchange no longer exists — what do I do about missing records?
Try to retrieve whatever you can from blockchain explorers using your old wallet addresses, email receipts from the exchange, or bank statements showing deposits and withdrawals. Where exact records are genuinely unavailable, document your efforts to retrieve them and use reasonable estimates with clear methodology. Any reconstruction should be transparent and conservative.
Do I need to keep records for tax years where I had no liability?
Yes. You need records to demonstrate that there was no liability — which requires showing that gains were below the annual exempt amount and proceeds were below £50,000. Loss years particularly need to be documented even if no tax was due, because those losses may be claimed later.
Is a CSV export from an exchange sufficient for HMRC?
A CSV export is good evidence but may not be sufficient on its own. For on-chain transactions, blockchain explorer data corroborating the exchange data strengthens your records. HMRC may also ask for evidence that exchange rates used were accurate — having a record of the price source you used is helpful.
How should I record transactions if I paid for something with Bitcoin?
Record the date, the item purchased, the quantity of Bitcoin spent, the GBP value of that Bitcoin at the time of purchase (your disposal proceeds), and the Bitcoin's cost basis (from your Section 104 pool). You may also want to retain the receipt from the merchant and the blockchain transaction hash as supporting evidence.
Can I use a crypto tax tool as my official record for HMRC purposes?
A reputable crypto tax tool that maintains a complete import history and shows its calculation workings is an excellent record-keeping system. The underlying exchange CSVs and API data are the primary source records; the tool is the aggregation and calculation layer. Both together give HMRC everything they would need in an enquiry.
Tool information accurate at time of writing.