Declare Crypto to HMRC: The Voluntary Disclosure Guide

HMRC has a dedicated Cryptoasset Disclosure Service for people who identify unpaid tax on cryptoasset income or gains from earlier periods. The difficult part is usually not opening the form. It is deciding the correct route and reconstructing figures that can be supported by the underlying exchange and wallet records.

This guide explains the current GOV.UK process, what calculation evidence is needed, and where a software tool must stop. It does not tell you which behaviour, penalty, or assessment window applies to your circumstances.

What the Cryptoasset Disclosure Service is

The service lets an individual tell HMRC about unpaid Capital Gains Tax or Income Tax connected with cryptoassets. HMRC's guidance says that current or previous-year income and gains may instead need to be reported on a Self Assessment return. The right route therefore depends on the year and the existing filing position.

An agent can submit a disclosure with temporary authorisation. That can be particularly important where the case covers several years, material amounts, offshore issues, company activity, trading status, or uncertainty about behaviour and penalties.

Read the current official process on GOV.UK: Tell HMRC about unpaid tax on cryptoassets.

The current process: calculate, submit, then pay

HMRC's cryptoasset guidance does not describe a separate registration of intent followed by a generic 90-day window. The current process is:

1. Gather the source evidence. Identify the exchanges, wallets, tax years, transactions, unpaid tax, interest, and applicable penalties.
2. Calculate the position. Separate income from capital activity and apply the UK share-matching rules across the relevant history.
3. Submit the disclosure. HMRC checks the submission and sends a payment reference.
4. Pay or contact HMRC. HMRC currently says payment is due within 30 days of submitting the disclosure. If full payment is not possible, contact HMRC using the official guidance.

The payment instructions and current deadline are set out on GOV.UK: Pay tax on cryptoassets.

Prompted and unprompted are fact-specific

HMRC describes an unprompted disclosure as one made when the person has no reason to believe HMRC has discovered, or is about to discover, the issue. Otherwise it is prompted. The timing and nature of HMRC contact can therefore matter, but the answer depends on the facts.

The quality of the disclosure, including telling HMRC, helping, and giving access to evidence, can also affect penalty reductions. Do not rely on a headline percentage, assume that reasonable care means no penalty, or describe a nudge-letter response as automatically unprompted.

See HMRC's prompted and unprompted disclosure guidance.

How many years may need to be considered

Assessment and disclosure periods depend on the tax, the filing history, behaviour, failure-to-notify rules, and whether offshore matters are involved. The familiar four-, six-, twelve-, and twenty-year references are not a menu for a taxpayer to choose from without analysis.

If several years are involved, or the behaviour is uncertain, ask a qualified adviser to define the scope before building the calculation. HMRC sets out the statutory time-limit framework in its Compliance Handbook.

The calculation evidence HMRC may need

A defensible cryptoasset calculation normally needs more than the year-end total shown by one exchange. Depending on the activity, it can include:

• the complete relevant acquisition and disposal history across owned wallets and exchanges;
• same-day matching, 30-day bed and breakfasting, and Section 104 pooling in the required order;
• GBP market values and their sources at the relevant times;
• income separated from capital activity;
• transfers between owned accounts distinguished from disposals;
• fees, manual adjustments, unresolved classifications, and missing source history kept visible.

Historic records are not always fully recoverable. Exchanges can close, exports can be incomplete, and off-chain trading cannot necessarily be inferred from wallet activity. A credible calculation names those gaps and records any reconstruction methodology rather than claiming completeness.

How ChainTax can support the calculation

ChainTax combines supported exchange imports and public-wallet activity in one UK calculation. It classifies supported DeFi activity, applies HMRC matching, and shows the pool movement, price source, confidence, and gain working for each disposal.

Low-confidence or incomplete evidence cannot unlock a positive accountant-review state. That makes the output useful as calculation evidence, but it does not turn the product into a disclosure adviser.

• ChainTax does not decide whether a disclosure is prompted.
• It does not choose the behaviour or penalty category.
• It does not submit the disclosure or tax return.
• It does produce a report, CSV, and per-disposal Show Working for supported activity.

Where CARF fits

In-scope providers began CARF due diligence, record keeping, and collection from 1 January 2026. Their first reports covering the 2026 calendar year are due to HMRC by 31 May 2027. That makes source reconciliation increasingly important, but it does not determine whether an individual disclosure is prompted or replace the facts of a specific HMRC contact.

Read the confirmed CARF timeline and the guide to what HMRC may see for the wider reporting context.

Questions