UK Crypto Self Assessment Deadline: 31 January 2027 Complete Guide

The 2025/26 UK tax year closed on 5 April 2026. If you disposed of any cryptocurrency during that year and your gains exceeded the £3,000 Capital Gains Tax allowance, you are required to report them to HMRC via Self Assessment. This guide walks through the key deadlines, what counts as a disposal, and the exact steps to avoid penalties.

Key dates for 2025/26 crypto tax

The tax year ran from 6 April 2025 to 5 April 2026. From the day the tax year ends, you have a series of deadlines. 5 October 2026 is the deadline to register for Self Assessment if you have not filed before. 31 October 2026 is the deadline for paper Self Assessment returns. 31 January 2027 is the deadline for online Self Assessment returns and for paying any tax owed. If you miss the online deadline, HMRC charges an automatic £100 penalty regardless of whether you owe any tax.

What counts as a crypto disposal

HMRC treats cryptocurrency as property, not currency. This means almost every interaction with your crypto can be a taxable event. Selling crypto for GBP or another fiat currency is a disposal. Swapping one token for another, including stablecoin conversions, is a disposal. Spending crypto on goods or services is a disposal. Gifting crypto to anyone other than your spouse or civil partner is a disposal. Moving crypto between wallets you own is not a disposal and does not trigger tax.

The £3,000 allowance and 18%/24% rates

Every UK taxpayer gets a Capital Gains Tax allowance of £3,000 for the 2025/26 year. Gains above this are taxed at 18% if you are a basic-rate taxpayer and 24% if you are a higher-rate taxpayer. The rates changed on 30 October 2024 from the previous 10%/20%, so any disposals on or after that date fall under the higher rates. If your total gains are below £3,000 but your total disposal proceeds exceed £50,000 (£50,000 for 2025/26), you still need to report them.

Pooling, same-day, and 30-day rules

HMRC requires Section 104 pooling — all units of the same token share a weighted average cost basis, not FIFO. Before the pool is used, two matching rules apply. The same-day rule matches any tokens bought and sold on the same day. The 30-day "bed and breakfasting" rule matches any tokens re-bought within 30 days of a sale. Getting these wrong is the most common way UK crypto investors overpay or underpay HMRC.

What to include on your return

On the Capital Gains supplementary pages (SA108) you report total disposal proceeds, total allowable costs, total gains, and total losses. HMRC expects you to keep records of every transaction — date, type, quantity, GBP value at the time, exchange, counterparty, and wallet addresses — for at least five years after the 31 January filing deadline.

Penalties for late filing

Miss the 31 January 2027 deadline and HMRC automatically charges £100. After three months the penalty increases by £10 per day up to a maximum of £900. After six months, HMRC adds the greater of £300 or 5% of the tax due. After 12 months, another £300 or 5% is added. Deliberate non-disclosure can attract penalties of up to 100% of the tax owed, and with CARF (the OECD's Crypto-Asset Reporting Framework) rolling out across the UK from January 2026, HMRC has unprecedented visibility into crypto activity.

How to calculate it all in minutes

Calculating Section 104 pooling, same-day matching, and 30-day rules across hundreds of transactions manually is practically impossible. CryptoLens automates the entire process: paste any wallet address, and the calculator applies HMRC's exact rules for the 2025/26 tax year. Export a fully formatted PDF for your SA100 in seconds.