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If you trade, invest, stake, or otherwise use crypto in the UK, HMRC expects you to keep clear and complete records of your activity. Good records are not only about calculating tax correctly. They are essential if HMRC ever asks you to explain how a figure was calculated, justify a disposal count, or evidence a disclosure.
Record-keeping has become more important in 2026 for two reasons:
- The 2025–2026 Self Assessment return contains a mandatory dedicated cryptoasset section, requiring specific figures that cannot be inferred from general totals.
- Exchanges are now reporting verified identity data and transaction data to HMRC under the Cryptoasset Reporting Framework (CARF).
This guide explains what records HMRC expects you to keep, how far back HMRC can ask for data, and how to prepare exchange and wallet records in a way that supports defensible tax reporting for UK resident individuals.
Record Keeping: What You Must Be Able to Show
Core Transaction Data
For every crypto transaction, HMRC expects you to be able to evidence:
- Date and time of the transaction
- Type of transaction (buy, sell, swap, transfer, reward, etc.)
- Asset disposed of and asset acquired
- Quantity of each asset
- GBP value at the time of the transaction
- Fees paid (including gas fees)
- Exchange or wallet used
- Transaction reference or hash
This applies across centralised exchanges, decentralised protocols, and self-custody wallets.
Valuation Methodology (Reasonable Care)
HMRC requires that crypto valuations are:
- Reasonable
- Consistent
- Verifiable
You must keep a record of:
- Which exchange or price source was used for GBP conversion (e.g. a specific exchange price, CoinMarketCap, CoinGecko)
- Whether the price used was spot, midpoint, or daily average
- Time alignment between transaction timestamp and price source
Warning: Switching valuation sources selectively to reduce tax exposure may be treated as careless. Consistency matters more than precision.
Income Records
Where crypto generates income (staking, mining, creator income, rewards), retain:
- Date income became accessible
- Asset and quantity received
- GBP value at receipt
- Source protocol or platform
- Related fees
Income must be valued at receipt, not when sold later.
Example: Minimum Record Set
Transaction
- Swap 0.5 ETH for SOL on a DEX
Records Required
- Timestamp
- ETH quantity disposed
- SOL quantity received
- GBP valuation source and price used
- Gas fee paid
- Transaction hash
- Wallet address
The Mandatory Cryptoasset Section (2025–2026 Returns)
The 2025–2026 Self Assessment return includes a dedicated cryptoasset section on the Capital Gains pages.
You must now separately report:
- Number of crypto disposals
- Total crypto proceeds
- Total crypto gains or losses
Crypto figures are no longer grouped under “other assets” alongside shares or property.
Your records must therefore support:
- Accurate counting of disposals
- Separate aggregation of crypto proceeds
- Reconciliation back to transaction-level data
If your records cannot produce these figures cleanly, HMRC may treat the return as incomplete or incorrect.
Applying the Matching Rules (30-Day Rule)
HMRC does not only expect a list of transactions. It expects evidence that the matching rules have been applied correctly.
This includes tracking:
- Same-day acquisitions
- 30-day repurchases (“bed and breakfasting”)
- Section 104 pooled holdings
Your records must be able to show whether the same token was repurchased within 30 days of a disposal, which acquisition was matched to which disposal, and how the cost basis was calculated.
Example: 30-Day Matching
What happens
- Sell 1 BTC on Day 1 for £30,000
- Buy 1 BTC again on Day 20 for £32,000
Tax rule
- The disposal must be matched to the Day 20 purchase
- The £32,000 cost applies, not the historic pooled cost
Your audit trail must evidence this logic clearly.
CARF and Identity Record-Keeping (2026)
As of 1 January 2026, exchanges are required to collect and verify:
- National Insurance number
- Tax residency
- Identity information
Under CARF, HMRC will cross-reference the NI number on your tax return with the NI number reported by exchanges.
Compliance Action:
You should retain records of what NI number and residency information you provided to each platform, along with confirmation emails or account screenshots where available. Mismatch between exchange data and tax returns is now a major compliance trigger.
How Far Back HMRC Can Ask for Records
HMRC can request records based on behaviour:
- Careless errors: up to 6 years
- Deliberate behaviour: up to 20 years
In practice, HMRC often requests full transaction exports, supporting working papers, valuation methodology, and reconciliation schedules. Records should be retained accordingly.
Building a Defensible Audit Trail
What HMRC Looks For
HMRC expects:
- End-to-end traceability
- Logical reconciliation
- Clear valuation source consistency
- No unexplained gaps
- Transparent assumptions
Typical Audit Trail Structure
- Raw exchange CSV exports
- Wallet transaction exports
- Consolidated ledger
- Pool and matching calculations
- Final tax summaries
Each step must be reproducible.
CSV Exports From Exchanges
What to Download:
- Trades
- Deposits and withdrawals
- Fees
- Rewards
Not sure where to find this? See our guide on How to Download Coinbase Transaction History.
Download regularly. Access may not be permanent.
Common CSV Issues
- Missing GBP prices
- Timezone ambiguity
- Symbol inconsistencies
- Merged transaction types
Preserve original files unchanged.
Wallet History and On-Chain Records
Retain:
- Wallet addresses
- Explorer exports
- Transaction hashes
- Gas fees
- Protocol notes
DeFi often requires interpretation beyond raw history.
Updated Record-Keeping Checklist (Jan 2026)
| Record Type | Reference | Why It’s Critical |
|---|---|---|
| Section 104 pool | CRYPTO22200 | Supports cost basis |
| 30-day matching | CG13350 | Prevents wash trading |
| Transaction hashes | CRYPTO10400 | Immutable evidence |
| Exchange CSVs | CRYPTO10400 | Exchange reporting |
| NI / tax ID | CARF (2026) | Data matching |
Spreadsheet Warning
HMRC has increased scrutiny of simple spreadsheets.
Pooling and matching logic is complex. HMRC often expects clear working papers, visible intermediate calculations, and traceable formulas.
If using spreadsheets:
- Document every calculation step
- Avoid manual overwriting
- Preserve version history
Final numbers without working logic are more likely to be challenged.
Common Misunderstandings
- “Only totals matter.”
- HMRC expects transaction-level evidence.
- “Valuation source doesn’t matter.”
- Consistency is essential. Switching sources to lower tax is high-risk.
- “Exchanges will keep my data forever.”
- Not guaranteed. Delisted tokens or closed accounts can lead to data loss.
- “Spreadsheets are always sufficient.”
- Only if fully auditable and logic is transparent.
Summary
- Dedicated crypto reporting now requires granular records.
- Matching rules (Section 104, 30-day rule) must be evidenced.
- Valuation methodology must be consistent and documented.
- CARF requires identity matching (NI number).
- Records may be requested for up to 20 years.
- Audit trails must be reproducible.
- Spreadsheet controls matter more than ever.
Strong record-keeping is now a core part of crypto compliance in the UK, not an optional administrative task.
Need help preparing your records?
BlockBooks acts as your permanent audit trail. We store every transaction, calculation, and exchange rate snapshot securely, so your records are always HMRC-ready.