Filing your cryptocurrency gains on your UK Self Assessment tax return is a legal requirement — and getting it wrong can result in significant penalties. In this complete step-by-step guide we explain exactly how to report crypto on your Self Assessment in 2026.
Do You Need to File a Self Assessment for Crypto?
You need to file a Self Assessment tax return if your total capital gains from all sources — including cryptocurrency — exceed your annual CGT exempt amount, or if your total income exceeds 100,000 pounds, or if you received crypto as income from staking, mining, or employment.
Even if your gains are below the exempt amount, you may still need to file if your total proceeds from disposals exceed four times the exempt amount — currently this means proceeds over approximately 50,000 pounds trigger a reporting requirement even if the actual gain is within the exemption.
Step 1: Gather All Your Transaction Records
Before you can complete your Self Assessment, you need a complete record of every crypto transaction in the tax year — every purchase, sale, trade, staking reward, airdrop, and transfer. Most UK investors use crypto tax software like Koinly to import this data automatically from exchanges and wallets.
The UK tax year runs from 6 April to 5 April. Ensure your records cover the entire period and include the date, amount, value in GBP at the time of each transaction, and any fees paid.
Step 2: Calculate Your Gains Using Share Pooling
HMRC requires UK investors to calculate their cost basis using share pooling — averaging the cost of all purchases of the same cryptocurrency rather than tracking individual lots. Crypto tax software handles this automatically, but it is important to understand the principle.
The 30-day rule also applies — if you sell crypto and repurchase the same asset within 30 days, the sale is matched against the repurchase price rather than your pool average. This prevents bed-and-breakfasting — selling to crystallise a loss then immediately repurchasing.
Step 3: Log In to Your HMRC Online Account
Access your Self Assessment tax return through your Government Gateway account at gov.uk. If you have not previously registered for Self Assessment, you must register before 5 October following the end of the tax year in which you had taxable crypto activity.
Step 4: Complete the Capital Gains Summary Pages
In your Self Assessment return, navigate to the Capital Gains Summary section. You will need to enter the total proceeds from all crypto disposals, your total allowable costs, and your net gain or loss.
Koinly and other crypto tax software generate a Capital Gains Summary report in exactly the format required by HMRC — making this step straightforward if you have kept good records.
Step 5: Report Crypto Income
If you received cryptocurrency as income — from staking rewards, mining, airdrops received in exchange for a service, or as employment payment — report this in the Additional Information section as miscellaneous income. The value is the GBP fair market value at the time you received it.
Step 6: Submit Your Return
The deadline for online Self Assessment submissions is 31 January following the end of the tax year. Filing late results in an immediate 100-pound penalty, with further penalties accumulating the longer the return remains unfiled.
What If You Have Made Mistakes in Previous Years?
If you have incorrectly reported or omitted crypto gains in previous tax years, make a voluntary disclosure to HMRC as soon as possible. HMRC treats voluntary disclosures far more leniently than cases it discovers independently — typically reducing penalties significantly and avoiding criminal prosecution.
Key Takeaways
- File a Self Assessment if crypto gains exceed your CGT exempt amount or proceeds exceed four times the exempt amount
- Gather complete transaction records for the full UK tax year — 6 April to 5 April
- HMRC requires share pooling cost basis calculation — crypto tax software handles this automatically
- Report crypto disposals in the Capital Gains Summary section of your Self Assessment
- Staking and mining income goes in the Additional Information section as miscellaneous income
- The online Self Assessment deadline is 31 January following the end of the tax year
- Make a voluntary disclosure for any errors in previous years — HMRC treats these far more leniently