Failed to Declare Income to HMRC? Penalties and Disclosure

If you fail to tell HMRC that you need Self Assessment or omit taxable income, HMRC can assess the tax, charge interest and impose penalties. The outcome depends on the tax lost, how late the disclosure is and whether the behaviour was reasonable, careless or deliberate.

Failure to notify

A person who becomes liable to tax not fully collected at source normally must notify HMRC by 5 October after the tax year. Failure-to-notify penalties are based on “potential lost revenue”—broadly the unpaid tax resulting from the failure.

Penalty ranges

Indicative statutory ranges can include:

Unprompted disclosure and full cooperation can reduce the percentage. Offshore matters can carry different or higher penalties.

Late filing penalties are separate

If HMRC issued a notice to file, penalties can include:

• an initial £100 after the filing deadline;
• daily £10 penalties after three months, up to £900;
• 5% of tax or £300 at six months;
• another 5% or £300 at twelve months;
• higher twelve-month penalties for deliberate withholding.

These can apply even where the failure-to-notify penalty is nil.

Late payment and interest

Unpaid tax attracts interest from the original due date. Late-payment penalties can arise at 30 days, 6 months and 12 months, generally 5% of the unpaid amount at each stage. Filing, notification and payment consequences accumulate separately.

How far back can HMRC assess?

Broadly, HMRC can assess up to:

• 4 years for ordinary underpayment;
• 6 years where loss was caused by carelessness;
• 20 years for deliberate behaviour, failure to notify and certain offshore cases.

The exact rule depends on the tax and facts.

What counts as taxable income to declare?

• self-employment and casual trading;
• rental income;
• savings and dividends above relevant treatment;
• foreign income;
• crypto and investment gains;
• tips, commissions and platform income;
• trust, estate and miscellaneous income;
• taxable benefits or pension charges not collected correctly.

Tax-free allowances can reduce liability, but gross-income tests can still create filing or record requirements.

HMRC data matching

HMRC receives information from employers, banks, Companies House, Land Registry, online platforms, crypto exchanges and overseas tax authorities. A return can be checked against these sources years later.

What to do before HMRC contacts you

1. Identify every missing tax year and income source.
2. Reconstruct records and calculate tax, interest and penalties.
3. Use the correct disclosure route.
4. Make a full, accurate unprompted disclosure.
5. Pay or request Time to Pay.
6. File outstanding returns where HMRC requires them.
7. Retain evidence and submission acknowledgements.

Which disclosure route?

The route depends on the issue:

• ordinary Self Assessment registration and late returns;
• HMRC Digital Disclosure Service for suitable direct-tax matters;
• Let Property Campaign for eligible landlords;
• Contractual Disclosure Facility where deliberate fraud is involved;
• specialist routes for offshore or other campaigns.

Using the wrong route can delay settlement. Obtain advice before admitting deliberate conduct.

Prompted versus unprompted disclosure

A disclosure is normally unprompted when made before HMRC has reason to suspect the specific issue. It usually attracts lower minimum penalty percentages. Once HMRC writes or opens a check, a disclosure can be prompted.

What if no tax was due?

Potential lost revenue may be nil where allowances, losses or payments eliminate tax, but a formal notice to file still creates filing penalties unless withdrawn. Submit or ask HMRC to withdraw the notice.

Reasonable excuse

A genuine unforeseen event can excuse late notification or filing if you act without unreasonable delay after it ends. Lack of knowledge is assessed in context but is not automatically accepted. Keep evidence.

Deliberate conduct

Concealing income, creating false documents or repeatedly ignoring known duties can lead to higher penalties, naming, security demands or criminal investigation. Stop and obtain specialist legal or tax advice.

Correcting an existing return

Amend online within the normal 12-month amendment window. After that, use the appropriate disclosure or claim route. Do not overwrite records or submit an incomplete amendment that omits connected errors.

Official guidance

• HMRC: failure-to-notify penalties
• HMRC: Digital Disclosure Service

This guide is general information. Deliberate or multi-year omissions require specialist advice.