What Happens If You Don't Report Crypto to HMRC?

Overview

Most people asking this question are not hardened evaders. They are someone who traded a lot in 2021, did not realise crypto-to-crypto swaps were disposals, and has been quietly hoping it does not matter.

It is worth answering properly, because the honest answer is more nuanced than either "nothing happens" or "you will go to prison". The penalty regime is graduated, and the single biggest variable is not how much tax is owed — it is whether you told HMRC before HMRC found out.

That variable has become considerably more urgent this year, for reasons covered below.

The Rules Changed on 1 January 2026

Until recently, HMRC's visibility into crypto activity was patchy. It relied on data requests to individual exchanges, information from other tax authorities, and the fact that money eventually reaches a bank account.

The Cryptoasset Reporting Framework changed that. It came into effect in the UK on 1 January 2026. UK cryptoasset service providers now collect and report user and transaction data annually, with the first reports covering calendar year 2026 and due to HMRC between 1 January and 31 May 2027. International exchanges of that data begin in 2027.

Two details matter for anyone weighing this up.

First, the UK went further than the international standard requires. The framework as drafted covers non-resident customers, and the UK extended it to collect information on UK-resident customers as well. Domestic activity is in scope.

Second, this is not a future risk to be reassessed later. Data for 2026 is already being collected. How CARF and DAC8 work covers the mechanics.

The Penalty Depends on Behaviour and Disclosure

HMRC's penalties for failure to notify are set as a percentage of the tax due. Two things determine where in the range you land: how the failure came about, and whether your disclosure was unprompted — meaning you came forward with no reason to believe HMRC was about to discover it — or prompted.

Behaviour	Unprompted minimum	Prompted minimum	Maximum
Non-deliberate, HMRC aware within 12 months	0%	10%	30%
Non-deliberate, HMRC aware after 12 months	10%	20%	30%
Deliberate	20%	35%	70%
Deliberate and concealed	30%	50%	100%

Read the top row carefully. A genuine mistake, disclosed voluntarily and reasonably promptly, can carry a penalty of nothing at all. The same mistake, disclosed only after HMRC comes asking, starts at 10% and can reach 30%.

At the other end, a deliberate and concealed failure can cost 100% of the tax on top of the tax itself.

Interest runs on the late tax regardless of which row applies. Penalties and interest are separate things, and both accrue.

Work out what you owe

How Many Years You Have to Go Back

This is where behaviour has its largest financial effect, and it surprises people more than the percentages do.

HMRC's cryptoasset disclosure service asks you to disclose:

• 3 years if you took reasonable care but still underpaid;
• up to 5 years if you did not take enough care;
• up to 20 years if the failure was deliberate.

The gap between three years and twenty years is usually far larger in cash terms than the difference between a 10% and a 30% penalty. Someone who traded heavily in 2021 and treats the position as a careless oversight is looking at a very different number from someone whose conduct is assessed as deliberate.

What the Disclosure Process Involves

HMRC operates a dedicated service for telling them about unpaid tax on cryptoassets, covering exchange tokens, NFTs and utility tokens.

The shape of it:

1. You work out the tax, interest and penalty you believe are due.
2. You make the disclosure and offer that amount.
3. HMRC sends a payment reference number within 15 working days.
4. Payment is due within 30 days of making the disclosure.
5. HMRC carries out checks and either accepts the offer or comes back to you.

One thing to note: if the unpaid tax relates to the current or a previous tax year for which you still need to file, the Self Assessment return is the right route rather than this service.

The 30-day payment window is worth planning for. Working out the liability first, rather than starting the process and calculating afterwards, avoids an uncomfortable deadline.

"They Will Never Match It to Me"

This reasoning had some force a few years ago. It has much less now, and the specific counterarguments are worth knowing.

Exchanges verified your identity. Any platform with KYC has your name, address and tax residence, and under the reporting rules is obliged to report them alongside your transaction data.

Blockchains are permanent and public. On-chain history does not expire. An address linked to a verified account at any point is linked from then on, in both directions.

Fiat has to land somewhere. Cashing out reaches a bank account, which is an entirely conventional source of information.

Data now arrives automatically. This is the real change. Previously HMRC had to ask. Now the reports come in annually whether or not anyone is looking at you specifically.

Practically, this also determines whether a later disclosure counts as unprompted. Once HMRC holds data suggesting undeclared gains, a disclosure made afterwards is harder to characterise as voluntary — and, as the table shows, that distinction is where most of the money is.

What You Might Not Owe

Not every unreported year produces a liability, and it is worth establishing that before assuming the worst.

• Gains below the annual exempt amount are covered by the allowance. The amount is £3,000 for 2026/27, but it was higher in earlier years — £6,000 in 2023/24 and £12,300 before that — so older years may be clear even where activity was significant.
• Losses may offset gains, and many people who traded through 2021 and 2022 have real losses they never claimed. A loss must be claimed within four years of the end of the tax year it arose in.
• Buying and holding is not a disposal. If you bought and never sold, swapped or spent, there may be nothing to report.
• Moving between your own wallets is not a disposal, though it does need recording.

A complete calculation sometimes shows a much smaller number than feared, and occasionally none. Which reliefs are available covers what can legitimately reduce the figure.

Calculate past tax years

The Practical Sequence

If you think you have unreported crypto activity:

1. Work out the actual position first. Import every exchange and wallet you have used, for every year concerned. Guessing produces either an overpayment or a disclosure that fails HMRC's checks.
2. Establish which years actually have a liability, after allowances and claimed losses.
3. Take advice if the numbers are large or the behaviour question is not clear-cut. The reasonable care versus careless versus deliberate distinction determines both the penalty band and how far back you go, and it is not a judgement to make casually about yourself.
4. Disclose before you are prompted. That is where the penalty range collapses toward zero.

Step one is the one people skip, and it is the one everything else depends on. Building a complete history is the whole job.

Conclusion

The realistic answer to what happens if you do not report crypto to HMRC: interest on the unpaid tax, a penalty of between nothing and 100% of it depending mostly on behaviour and on who moved first, and a disclosure reaching back three, five or twenty years on the same basis.

The regime is deliberately built so that coming forward is much cheaper than being found. With annual reporting now live, the odds on the second outcome have shifted substantially.

If you are unsure whether you owe anything, the first move is not a disclosure — it is a calculation.

Generate a UK tax report

Official Resources

• GOV.UK: tell HMRC about unpaid tax on cryptoassets
• HMRC: penalties for failure to notify — maximum and minimum penalties (CH73200)
• HMRC: unprompted or prompted disclosure (CH73140)
• GOV.UK: your guide to making a disclosure
• GOV.UK: implementation of the Cryptoasset Reporting Framework
• GOV.UK: Capital Gains Tax allowances

This article provides general information and is not tax advice. Whether a failure is treated as non-deliberate, careless or deliberate has significant consequences; take professional advice before making a disclosure.