How to Declare Undeclared or Late Crypto Gains (UK Disclosure Guide)

Amendment vs Disclosure

Before starting a disclosure, check whether the return can still be amended.

• A Self Assessment return can normally be amended up to 12 months after the filing deadline.
• For the 2024–2025 tax year, this means amendments are usually possible until 31 January 2027.

If the amendment window has closed, or if no return was filed when one should have been, a formal disclosure is required.

HMRC Disclosure Facilities

Cryptoasset Disclosure Service (CDS)

The Cryptoasset Disclosure Service (CDS) is now the default route for crypto-specific disclosures.

It applies to:

• Historic crypto errors
• Missed gains or income
• Incorrect reporting across multiple years

Although CDS was originally launched to sweep up older historic errors, it is now used for most pure crypto disclosures.

Digital Disclosure Service (DDS)

The Digital Disclosure Service (DDS) remains available where:

• Errors span multiple income types (e.g. crypto plus rental or self-employment), or
• A broader disclosure is required

The 90-Day Clock (Critical)

This includes:

• Calculations
• Supporting records
• Payment or payment proposals

If you miss the 90-day deadline:

• You may lose “unprompted” status
• HMRC may open a formal enquiry
• Penalty exposure increases

Practical point: Do not notify HMRC until your calculations and records are substantially ready.

Voluntary Disclosure and Timing

Why Timing Matters More in 2026

As of 1 January 2026, CARF data collection is live across exchanges. The first large data exchange to HMRC is expected by May 2027.

HMRC has indicated that:

• Once CARF data is received, disclosures involving that data may be treated as prompted, even if you initiate them
• Prompted disclosures carry materially higher penalties

Unprompted vs Prompted Disclosure

Unprompted Disclosure

You come forward before HMRC contacts you or matches your data.

Prompted Disclosure

HMRC contacts you first or already holds matching evidence.

Penalty outcomes differ significantly.

Updated Penalty Ranges (Indicative)

Exact outcomes depend on cooperation, record quality, and accuracy of disclosure.

What You Need to Prepare

A disclosure typically requires:

• A list of affected tax years
• Capital gains and income calculations for each year
• Exchange statements and wallet records
• GBP valuation methodology
• Explanations of how errors arose
• Reconciliation to totals where possible

Clarity and consistency matter more than perfection.

Back Taxes, Interest and Payment

How Far Back HMRC Can Assess

• Careless behaviour: normally up to 6 years
• Deliberate behaviour: up to 20 years

Most retail crypto cases fall into the careless category.

Interest on Back Taxes

Interest accrues from the original due date until payment.

Paying What You Owe

HMRC expects either:

• Payment in full, or
• A Time to Pay arrangement

Where voluntary disclosure is made and the balance exceeds £30,000, HMRC will often consider staged repayment over up to 12 months, subject to affordability evidence.

The Myth of a Crypto “Amnesty”

There is no crypto tax amnesty in the UK.

Disclosure does not:

• Cancel tax
• Cancel interest
• Guarantee zero penalties

What disclosure does provide:

• Lower penalty ranges
• Faster resolution
• Reduced enforcement risk

When people refer to an “amnesty”, they usually mean penalty mitigation — not tax forgiveness.

Compliance After Disclosure

After disclosure:

• Future returns should be accurate and complete
• Records should be maintained properly
• Any uncertain areas should be documented

Repeat errors materially increase penalty exposure.

Common Misunderstandings

“I should notify HMRC immediately.”

Prepare first; the 90-day clock is unforgiving.

“CDS is only for old years.”

It is now the default crypto disclosure route.

“I can wait until HMRC writes to me.”

That converts the disclosure to prompted with higher penalties.

“Current interest rate applies to everything.”

Interest depends on the rate in force during each unpaid period.