HMRC Small Business Tax Gap: What It Means for Sole Traders and the Self-Employed

Tax Queen

Tax Expert @ Pie

4 min read

Every year, HMRC publishes a figure that gets surprisingly little attention outside of tax circles: the tax gap. It tells you how much tax was owed across the UK and how much actually got paid. The difference between the two numbers is enormous, and for the past several years, small businesses have sat firmly at the top of the list of contributors.

In 2024–25, the HMRC small business tax gap reached a record £59.2 billion. If you are self-employed, a sole trader, or running a small business, understanding what drives this figure and why it puts you in HMRC's line of sight is worth your time. Not because you are doing anything wrong, but because most of the gap comes from errors rather than deliberate evasion, and errors can happen to anyone.

What Is the Tax Gap and How Does HMRC Measure It?

The tax gap is the difference between the amount of tax HMRC expects to collect and the amount it actually receives. It is not a measure of fraud alone. It captures everything from deliberate evasion to honest mistakes, late payments, legal avoidance, and cases where a business simply could not pay what it owed.

HMRC has been measuring the tax gap since 2005–06, when it stood at 7.5% of all tax due. The long-term trend has been downward, reflecting improvements in digital reporting, better data access, and stronger enforcement. In 2024–25, the gap came in at 6.4%, representing £59.2 billion out of a total tax liability of £865.2 billion. Put another way, HMRC collected 93.6% of everything owed that year, but the remaining fraction still added up to a figure close to the annual NHS capital budget.

The figures are published annually and revised over time as more data becomes available. HMRC uses a range of methods to estimate the gap, including analysis of tax returns, third-party data, and compliance checks. It is a planning tool as much as a performance measure, helping the department decide where to focus its resources. You can read more about how HMRC approaches compliance checks and what they involve.

Why the Small Business Tax Gap Is the Largest of Any Group

Of the £59.2 billion gap recorded in 2024–25, small businesses were responsible for 62% of the total. That makes the small business tax gap the single largest share across all taxpayer groups, ahead of large businesses, wealthy individuals, and criminal activity.

This is not a new pattern. Small businesses have consistently topped this table for years. The reasons are partly structural. Sole traders and small business owners manage their own tax affairs without payroll departments or dedicated finance teams. Income can be variable, expenses are often mixed between business and personal use, and the rules around what is allowable are not always straightforward.

The 2024–25 figures also showed a sharp rise from the previous year, when the gap stood at £52.8 billion or 6% of tax due. The increase reflects both a growing number of self-employed filers and the ongoing complexity of the tax system they are navigating.

If you are unsure whether your records and returns meet HMRC's expectations, it is worth reading about what triggers an HMRC investigation so you know what to watch for.

Self-employed woman using a calculator to organise receipts and tax paperwork on a desk

Tax Evasion vs Tax Errors: What Actually Drives the Gap

A common assumption is that the small business tax gap is mostly driven by deliberate evasion. The data tells a different story. Tax evasion, where someone knowingly hides income or falsifies records, accounted for around 12% of the 2024–25 gap. That is significant in absolute terms, but it means the large majority of missing tax comes from other causes entirely.

The biggest drivers are what HMRC calls failure to take reasonable care, which covers mistakes on returns, and legal interpretation differences, where a taxpayer and HMRC disagree on how a rule applies. Hidden economy activity and criminal attacks make up smaller portions.

For most sole traders and freelancers, the realistic risk is not deliberate evasion. It is miscategorising an expense, missing a source of income, or applying a relief incorrectly. These are honest mistakes, but they still contribute to the HMRC small business tax gap and they can still attract a compliance check. Understanding what counts as undeclared income is one of the most practical steps you can take to make sure your returns are complete.

What This Means Practically: More Staff, More Checks, More Scrutiny

The government's response to a rising tax gap is more enforcement, not less. HMRC has been allocated £1.7 billion over four years to fund an additional 5,500 compliance staff and 2,400 debt management staff. That is a substantial expansion of the department's capacity to open enquiries, issue compliance letters, and pursue unpaid tax.

HMRC is also investing heavily in data matching and risk profiling, which means it can cross-reference your Self Assessment return against bank data, third-party income reports, and previous filings more efficiently than ever before. If something looks inconsistent, a letter is more likely to follow than it would have been five years ago. If you want a clearer picture of what you are likely to owe before you file, our self-employed tax calculator can help you estimate your bill and plan ahead.

This does not mean every small business should expect an investigation. But it does mean that the days of filing a return and hoping it goes unnoticed are firmly over. HMRC has both the tools and the staffing to look more closely at the sectors and taxpayer groups where the small business tax gap is largest, and self-employed filers are near the top of that list.

Pie is self-assessment software built to help sole traders stay on top of exactly this kind of scrutiny. You can find out more about the approach on the Why Pie page.

How to Protect Yourself: Records, Returns, and the Right Software

The most effective protection against HMRC scrutiny is also the most straightforward: accurate records and a correctly filed return.

For sole traders and self-employed individuals, this means keeping receipts and invoices, recording all income including cash payments and income from multiple sources, separating business and personal expenditure clearly, and keeping those records for at least five years after the 31 January filing deadline for the relevant tax year.

It also means being consistent. HMRC's data matching is particularly good at identifying discrepancies between years, or between what you have reported and what third parties such as banks or platforms have reported on your behalf. A return that looks very different from the previous year without explanation is more likely to attract attention.

How Pie works is built around exactly this kind of accuracy. Pie is self-assessment software designed for sole traders and self-employed individuals who want to file correctly without spending hours on admin. It helps you organise income and expenses, claim the right reliefs, and submit a return you can stand behind.

Notebooks, sticky note and pens laid out on a desk representing organised record keeping for small business tax

Filing Accurately Is the Best Response to the HMRC Tax Gap

The UK small business tax gap is a structural problem, and closing it is a long-term project for HMRC. But for individual sole traders and small business owners, the headline figure carries a clear message: this is a group HMRC is watching closely, and it has more resources than ever to act on what it finds.

Most people contributing to the gap are not criminals. They are busy self-employed individuals trying to manage their tax alongside everything else their work demands. The solution is not to live in fear of a compliance letter. It is to file accurately, keep good records, and use tools that make it easier to get things right. Find out more about Pie, or if you are ready to take the first step, try Pie today.