31 January is not a soft deadline. Miss it and you get an automatic £100 penalty even if you owe no tax at all. Wait too long and penalties escalate to 5% of any unpaid tax. The good news: getting your crypto figures together in time is much easier than most people expect.
Key dates for 2024/25
Do you need to file Self Assessment for crypto?
You must file a Self Assessment return if any of the following apply:
- —Your net capital gains exceed the £3,000 annual exempt amount
- —Your total disposal proceeds from all assets exceed £50,000 (even if gains are below £3,000)
- —You received crypto income (staking, mining) above the £1,000 miscellaneous income allowance
- —You are already registered for Self Assessment for any other reason (self-employment, rental income, etc.)
If you are below all thresholds and have no other reason to file, you have no legal obligation — but keep records for at least six years.
What happens if you miss the deadline
Late filing penalties for Self Assessment:
- —1 day late: £100 automatic penalty (regardless of whether tax is owed)
- —3 months late: additional £10/day penalty up to £900
- —6 months late: additional 5% of the tax owed or £300 (whichever is greater)
- —12 months late: a further 5% or £300
Interest is also charged on unpaid tax from 1 February 2026 at HMRC's current rate. Even if you cannot pay the tax in full, filing on time reduces the penalty burden significantly.
How to get your crypto figures ready in time
The most common reason people miss the deadline is that gathering transaction history from multiple exchanges takes longer than expected. Start early:
- —Export your transaction history from every exchange you have used
- —Gather records for any DeFi activity, NFT trades, or staking rewards
- —Import into Polyconomic to calculate your gain — you can see the figure for free
- —If you need the SA108-compatible PDF report, a Standard plan gives you access before the deadline
Frequently asked questions
I have never filed Self Assessment before. Do I need to register first?
Yes. If this is your first Self Assessment return, you must register with HMRC first. The deadline to register for the 2024/25 tax year is 5 October 2025. You will receive a Unique Taxpayer Reference (UTR) which you need to file. Registration can take up to 10 days to process.
What if I genuinely cannot pay the tax by 31 January?
File your return on time regardless of whether you can pay. This avoids the late filing penalty. Then contact HMRC to arrange a Time to Pay agreement, which lets you pay in instalments. Interest will still apply to any late payment, but the filing penalties are avoided.
Do I need to report previous years where I did not file crypto gains?
Yes, if you had taxable gains or proceeds above the thresholds in previous years and did not report them. HMRC allows voluntary disclosure of earlier years through the Let Property Campaign or directly. Acting proactively typically results in lower penalties than being investigated.
If I had losses last year but did not report them, can I still claim them?
You have four years from the end of the tax year to claim losses. So losses from 2021/22 (ending April 2022) can still be claimed until April 2026. After that window closes, the losses are permanently lost for tax purposes.
I am self-employed and already file Self Assessment. Do I just add crypto there?
Yes. If you are already registered for Self Assessment, add your crypto gains on form SA108 (Capital Gains Summary) as part of your existing return. Crypto income (staking etc.) goes on the SA100 under other income. Do not file a separate return.
Is there a way to get an extension on the 31 January deadline?
No automatic extension exists. HMRC may accept a reasonable excuse for late filing in exceptional circumstances (serious illness, natural disaster, HMRC system failure), but these are assessed case by case and are not guaranteed. Planning ahead is the only reliable approach.
General information only. Check HMRC's website for current deadlines and penalty rates.