Missed the HMRC Deadline? You’re Not Alone

It’s now May, and for many people across the UK, Self Assessment may no longer be top of mind. If the deadline has slipped by, don’t panic—but do act quickly.

HM Revenue & Customs (HMRC) applies automatic penalties for late tax returns, but there are clear steps you can take to reduce the impact and get back into compliance.

Today's blog explains what happens if you miss the deadline, how penalties work, and what to do next.

HMRC Self Assessment Mistake? Costs, Penalties & How to Get Back on Track

If your tax return is late, HMRC applies penalties automatically:

• £100 fixed penalty immediately after the deadline

• Further penalties if the return remains unfiled

• Daily penalties (around £10 per day) after 3 months (in some cases)

Even if you owe no tax, the initial penalty still applies.

The longer the delay, the more the penalties can increase.

What Happens If You Miss the Self Assessment Deadline?

In some cases, yes.

HMRC may reduce or cancel penalties if you have a reasonable excuse, such as:

• Serious illness or medical emergency

• Bereavement

• Unexpected technical failures

• Events beyond your control

However, general forgetfulness or being too busy is usually not accepted.

Supporting evidence is often required.

Can HMRC Penalties Be Cancelled?

You may need to complete a Self Assessment if you are:

• Self-employed or a sole trader

• A landlord

• Earning untaxed income (freelance or side work)

• Receiving dividends or investment income

• Involved in cryptoasset transactions (where taxable)

If you’ve never filed before, you must first register with HMRC to receive your Unique Taxpayer Reference (UTR).

Who Needs to File a Self Assessment?

One of the most common tax questions is what you can claim as expenses.

HMRC generally allows costs that are wholly and exclusively for business use, such as:

• Office and software costs

• Travel for business purposes

• Phone and internet (business portion)

• Marketing and advertising

• Accountancy fees

If you work from home, you may be able to claim a portion of household costs.

However, personal expenses are not allowed.

Incorrect claims can increase the risk of HMRC enquiries.

Allowable Expenses (What You Can Claim)

Capital Gains Tax (CGT) may apply when you sell assets such as property, shares, or investments.

Key points:

• You may pay tax on profits when selling assets

• There is an annual tax-free allowance (subject to change)

• Property disposals often have strict reporting deadlines

• Failing to report gains on time is a common mistake—and can lead to penalties.

Capital Gains Tax in Simple Terms

An HMRC investigation does not always mean wrongdoing.

Common triggers include:

• Errors or inconsistencies in tax returns

• Unusual expense claims

• Random compliance checks

• Third-party data matching

• There are two main types:

• Aspect enquiries (specific issue)

• Full enquiries (full review of tax affairs)

If contacted, respond promptly and keep records organised.

HMRC Investigations: What Triggers Them?

If you’ve missed a deadline or think something is wrong, the key is to act quickly:

• Submit your overdue return as soon as possible

• Check your HMRC account for penalties

• Pay any tax due or arrange payment

• Seek professional advice if needed

Delays usually increase both penalties and stress.

How to Get Back on Track

Missing a tax deadline is more common than many people realise—especially when life gets busy.

The important thing is that HMRC provides routes to correct the issue, reduce penalties where possible, and regain compliance.

If you are unsure where you stand, getting professional advice early can make a significant difference. At The Tax Faculty, we’re here to help you navigate your financial responsibilities with confidence and clarity. Get in touch today to see how we can support you.

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Final Thoughts

Capital Gains Tax Expertise: The Tax Faculty LLP Managing Partner Charles Tateson Named UK Capital Gains Tax Advisor of the Year 2023

The Finance Monthly Taxation Awards recognises the achievements of tax professionals from around the globe.

Winning such an award is no small feat. It is a reflection of hard work, extensive knowledge, and an ability to navigate the intricacies of the UK tax system.

Read more about Charles and the award here.

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