You can swap ETH for USDC on Uniswap in minutes. You approve the token, pay gas, and move USDC back to an exchange.
Months later, your Self Assessment records may contain wallet transactions and a contract call. No single statement may explain the full swap.
DEX vs CEX: Record-keeping burden for UK taxpayers: DEX activity usually creates more work. No platform gives you one complete, tax-ready history. CEX CSVs help, but you must still match wallet transfers.
Why HMRC needs evidence beyond a trade list
HM Revenue & Customs (HMRC) needs records that support your Self Assessment figures. A trade list alone may not be enough.
A disposal happens when you sell, swap, spend, or give away a cryptoasset. A disposal can trigger capital gains tax (CGT).
Your records must explain what happened and why.
A transaction is not always one tax event
One DEX action can create several pieces of evidence. A swap can include approval, tokens sent, route tokens, tokens received, and a gas payment.
An approval often lets a smart contract access your tokens. It is not usually a disposal. Still, label it and keep the record.
A blockchain entry is not a full tax explanation.
Own-wallet transfers still need proof
A transfer between wallets you own is usually not a disposal. You still need an audit trail.
Keep both wallet addresses, the transaction hash, date, and quantity. Add a note that confirms you controlled both wallets.
HMRC's ability to review crypto activity does not depend on contacting an exchange first. It also does not depend on tracing every wallet successfully.
HMRC may get data from UK-facing platforms. It may also examine public blockchain transactions. A public address alone does not prove control or explain a transfer.
You must keep records that support your Self Assessment crypto figures. These include costs, dates, GBP values, fees, wallet ownership, and disposal details.
An exchange withdrawal may be a transfer to your own wallet. It could also be a payment to someone else or a move to a DEX.
Only linked records can show the right CGT treatment. Reconcile records promptly, even if HMRC has not contacted you.
DEX vs CEX: evidence burden at a glance
A CEX cuts the starting workload for most people. A DEX leaves you to collect and join most evidence yourself.
| Evidence point | CEX: Coinbase or Kraken | DEX: Uniswap from own wallet |
|---|
| Download cost | Usually £0 for CSV export | Usually £0, but no native tax CSV |
| Records supplied for one swap | Order ID, time, pair, quantity and fee | Hash, token flows and gas on-chain |
| Typical manual review | About 2 to 5 minutes if funds stayed on-platform | About 5 to 15 minutes for a simple swap |
| GBP value evidence | Often needs adding or checking | You must select and retain a price source |
| Harder cases | Deposits, withdrawals and multiple accounts | Bridges, LP tokens, farming and failed transactions |
| Best fit | Most investors and frequent spot traders | Users prepared to keep event-level evidence |
A CEX CSV cannot usually show where a withdrawal went. It cannot tell you if it reached MetaMask, another exchange, or someone you paid.
A CSV may lack a reliable GBP value at the exact event time. It cannot include a disposal made away from the exchange.
The same £1,000 ETH-to-USDC Uniswap trade needs several records. Keep the wallet address, hash, ETH sent, USDC received, gas paid, execution time, and GBP value evidence.
For most UK taxpayers, a CEX creates fewer records for normal buying and selling. It is not a full answer. Match each deposit and withdrawal with your wallets. Then add GBP values and the transaction purpose. Use a DEX only when its trading or DeFi use justifies an event-by-event evidence file. Choose the route you can explain clearly five years later.
Keep records for each event. Do not rely on one exchange statement.
For each purchase or sale, keep the date, time, asset, quantity, fee, and GBP value. Keep the platform or wallet details too. Save the order ID or transaction hash.
For a swap, retain both sides as disposal evidence. Record the asset you gave up and the asset received. Link own-wallet addresses and confirm beneficial ownership.
For an airdrop, staking reward, loan, bridge, or liquidity-pool action, record the protocol, its purpose, quantity, GBP value, and your valuation evidence.
This approach works when CEX or DEX histories have gaps. It also prepares you for the more complex records that DeFi can create.
CEX records suit straightforward trading
A centralised exchange (CEX) suits investors who buy, sell, and hold on one or two platforms. It gives account statements, order histories, and downloadable CSV files.
These files are useful raw evidence for CGT calculations. They also help with Section 104 holding records.
CEX records reduce paperwork. They do not remove it.
Pros of using a CEX for records
- Coinbase and Kraken can give trade, deposit, and withdrawal histories from your account.
- A platform order ID links a trade to a named account and timestamp.
- Monthly exports can take between 2 and 10 minutes per platform when activity is limited.
Limits and who should avoid it
A CEX record is incomplete when your money moves beyond that exchange. You must match each deposit and withdrawal with the other side.
The most frequent mistake is treating every withdrawal as a sale. A withdrawal to your own wallet is usually not a disposal.
Use a dated logbook to keep files and wallet notes in one place. It helps you link transfers and note unusual DeFi actions as they happen.
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Our recommendation
A dated transaction logbook can keep wallet notes and exported files together. It works best for transfer links and unusual DeFi notes.
- Keeps transaction hashes beside each related exchange withdrawal or deposit
- Creates a written ownership trail for self-custody wallet addresses
- Keeps price-source and transaction-purpose notes for later tax checks
Check availability →
Choose a CEX if you make ordinary spot trades and can reconcile monthly. Avoid relying on it alone if you often send funds across wallets.
DEX records need an event file
A decentralised exchange (DEX) suits you only if you can keep evidence for each major on-chain action. A smart contract trades directly from your wallet.
No account provider will give you one joined-up statement. You must build that record yourself.
A DEX gives control, but it shifts the paperwork to you.
Pros of a DEX for active users
A DEX can offer tokens, pools, or routes that a CEX does not offer. It can suit active users who already save wallet and contract evidence.
A clear event file can make later review possible. Save records when you make the transaction, not months later.
This works well in theory, but it often fails in practice. People save the swap and forget gas, approvals, and bridge records.
Risks from bridges and liquidity pools
Bridges and liquidity pools create the greatest paperwork risk. One action can change chain, token form, and economic exposure.
Keep source and destination hashes for every bridge. Record deposited tokens, LP tokens received, rewards, withdrawals, and each valuation.
Complex DeFi records must explain the economic sequence. A final wallet balance cannot do that.
For wraps, keep the transaction that changed ETH into WETH. Label it separately from a swap.
For a Uniswap multi-hop route, save its swap records and route tokens. Keep token-in and token-out amounts, execution time, and transaction hash.
Route tokens may not stay in your wallet. Keep gas evidence for approvals, failed transactions, and completed contract calls.
Gas costs may matter to your calculation, depending on the facts. Do not assume all gas has the same treatment.
When you provide liquidity, record deposited tokens and LP tokens received. Keep pool rewards, farming receipts, and later withdrawal records.
For a bridge, keep both chain hashes and addresses. Record the token form received on the new chain.
Choose a DEX only if you can maintain this evidence as you trade. The next section turns that choice into a workable monthly routine.
Choose your route by trading pattern
Choose a CEX for lower admin work. Choose a DEX only where its function is worth the extra evidence work.
A simple investor usually needs fewer records on a CEX. A frequent DeFi user needs a routine, not a last-minute spreadsheet.
Your records are strongest when you update them each month.
Use this monthly reconciliation routine
- Export: Download CSV and PDF histories from every CEX. Export wallet transactions or save explorer links.
- Label: Mark each entry as a buy, sale, swap, own transfer, income, bridge, wrap, liquidity action, or gas.
- Match: Link every exchange deposit and withdrawal to a wallet, platform, or disposal.
- Value: Keep one consistent GBP price source for each relevant date and time.
- Back up: Save files, hashes, and notes in two places. Keep them for at least five years after the 31 January filing deadline.
Get professional help when records are high-value, incomplete, or uncertain. This is especially true for lending, liquidity pools, and frequent cross-chain activity.
A common case involves a trader using Kraken and MetaMask. They later use a bridge and a liquidity pool. Their CSV looks tidy, but it cannot explain the missing assets.
Choose the CEX route unless you need a DEX feature. If neither route fits cleanly, reduce new activity and rebuild your evidence first.
This comparison matters less if you only hold crypto on one UK platform. It also matters less if you made no withdrawals, swaps, staking, transfers, or DeFi transactions. Match the platform's full history to your own records. This is not tailored tax advice for high values, uncertain facts, or complex DeFi arrangements.
What people ask
Can HMRC track crypto wallets?
HMRC can obtain exchange data and examine public blockchain activity. Keep wallet addresses, hashes, and ownership records.
Is a DEX harder for UK crypto tax records?
A DEX is usually harder because each swap needs token, gas, wallet, hash, and GBP-value evidence. Bridges and pools need even more linked records.
Is a CEX CSV enough for a tax return?
No, if you used other wallets or platforms. Match transfers and keep GBP values, fees, and acquisition costs.
Do own-wallet transfers create CGT?
Own-wallet transfers are usually not CGT disposals when beneficial ownership stays the same. Keep both addresses and the transaction hash.
Do I need to save failed crypto transactions?
Yes, save failed transactions when they used gas or explain missing token movements. Record the hash, GBP value, and purpose.
Are Uniswap liquidity pools one transaction?
No, liquidity-pool deposits, LP-token receipts, rewards, and withdrawals can need separate records and values. Save evidence for each event.
How long must UK crypto tax records be kept?
Keep Self Assessment records for at least five years after the 31 January submission deadline. Keep files and notes in two places.
A tax tool can cut sorting time, but you must check its labels. Review bridges, approvals, LP tokens, and gas carefully.
- The key point: CEX trading usually means less paperwork, but exports still need transfer matching.
- For DEX activity: DEX activity needs proof of the full economic event, not only a visible swap.
- For your records: Keep hashes, GBP values, ownership proof, and purpose notes while events remain fresh.
- In practice: Reconcile monthly or quarterly, well before you prepare Self Assessment.
Learn more
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