Does HMRC Check Self Assessment Returns? UK Guide 2026

Yes. HMRC checks Self Assessment returns using automated risk analysis, third-party data and formal compliance enquiries. A check does not automatically mean wrongdoing, but taxpayers must provide accurate records and respond by the stated deadline.

How HMRC selects returns

• figures that differ from earlier years or sector benchmarks;
• information from employers, banks, platforms, Companies House or overseas authorities;
• large or unusual expense, loss or repayment claims;
• property, crypto, offshore or cash-business risk indicators;
• inconsistencies between VAT, PAYE, CIS and Self Assessment;
• random or targeted compliance campaigns;
• reports from third parties.

HMRC does not publish its full risk model. A return can be correct and still be selected.

Types of check

Aspect enquiry: focuses on one or more entries, such as expenses or property income.

Full enquiry: reviews the return and underlying records more broadly.

Information check: HMRC may ask about a discrepancy or request documents without immediately opening a formal enquiry.

Normal enquiry window

HMRC normally has 12 months after the return is filed to open an enquiry. Where a return is submitted late, the window can run to the next quarter date under statutory rules. Separate discovery-assessment time limits can extend beyond the enquiry window where income was omitted or tax underpaid.

Discovery time limits

Broadly, HMRC can assess:

• up to 4 years for an ordinary error;
• up to 6 years where the loss of tax was caused by carelessness;
• up to 20 years for deliberate behaviour, failure to notify and certain offshore cases.

Exact limits depend on tax, behaviour and facts.

What HMRC can request

• bank and card statements;
• sales invoices and purchase receipts;
• mileage, home-use and expense calculations;
• rental records and mortgage statements;
• investment and crypto transaction histories;
• foreign income and tax evidence;
• contracts, diaries and business records;
• explanations of estimates and accounting treatment.

An information notice must be reasonably required to check the tax position. Privileged legal advice and purely personal records have protections, but professional advice may be needed before refusing.

What happens after a letter arrives?

1. Check whether it is genuine through official HMRC contact details.
2. Note the scope and response deadline.
3. Preserve all paper and digital records.
4. Compare the return with source data and identify errors.
5. Respond clearly, supplying indexed evidence.
6. Ask for clarification or reasonable extra time if necessary.
7. Keep copies of every communication.

Can you amend the return?

A return can normally be amended within 12 months of the filing deadline. Once an enquiry is open, disclose errors to the officer rather than assuming an online amendment ends the matter. A voluntary disclosure can reduce penalties.

Penalties for inaccuracies

Penalties are based on potential lost revenue and behaviour:

• reasonable care: generally no inaccuracy penalty;
• careless: normally 0%–30%;
• deliberate but not concealed: normally 20%–70%;
• deliberate and concealed: normally 30%–100%.

Offshore matters can carry higher ranges. Quality, timing and whether disclosure was prompted affect the percentage.

Interest and tax

Additional tax attracts interest from the original due date. HMRC can also adjust payments on account and connected years. Conversely, an enquiry can confirm the return or produce a repayment.

Meetings and visits

HMRC may request a meeting or business-records visit. Ask for an agenda and understand whether attendance is voluntary. An adviser can attend. Do not speculate; provide accurate answers and follow up in writing.

Closure notices and appeals

HMRC ends a formal enquiry with a closure notice stating conclusions and amendments. The taxpayer can appeal within the deadline, normally 30 days, request a statutory review or notify the tax tribunal.

Data HMRC already receives

HMRC receives PAYE and pension reports, bank interest, property and company information, platform-seller data, Common Reporting Standard information and other records. Pre-populated figures still need checking.

How to reduce risk

• reconcile all income to bank and third-party statements;
• retain receipts and calculations;
• separate business and private transactions;
• explain estimates and unusual entries;
• disclose uncertain tax positions appropriately;
• correct errors before HMRC contacts you;
• use a competent adviser for complex matters.

Related: Self Assessment records to keep.

Official guidance

• HMRC: tax compliance checks
• HMRC: inaccuracy penalties

This guide is general information. Obtain professional advice for formal enquiries or information notices.