Australia's estimated net tax gap reached $58.2 billion for 2022–23, with small business accounting for the largest share.

The small business component was estimated at $27.2 billion, representing close to half of the total net gap.

The figures are particularly relevant as tax administration increasingly relies on contractor reporting, digital-platform information, pre-filled data and broader data-matching programs to identify income that may have been omitted from tax returns.

What the $58.2 Billion Tax Gap Measures

The tax gap is the estimated difference between the amount of tax that would be collected if taxpayers fully complied with the law and the amount actually collected.

For 2022–23, the net tax gap was estimated at $58.2 billion.

That represented approximately 9.1% of around $640 billion in theoretical tax liabilities.

Put another way, about 90.9% of the tax theoretically payable was collected.

The gross tax gap, measured before additional amounts recovered through compliance activity, was higher at approximately 10.4%.

These estimates relate to 2022–23 rather than the current financial year because tax-gap calculations require substantial reporting and compliance data before they can be finalised.

Why Small Business Is the Largest Component

Small business represented the biggest individual segment of the tax gap.

Its estimated net gap was $27.2 billion.

Individuals not in business accounted for approximately $12.5 billion, while the GST gap was about $8.1 billion.

Large corporate groups accounted for a considerably smaller amount.

Small business therefore represented roughly 47% of the overall net tax gap.

Its estimated income tax gap was also relatively high as a proportion of theoretical liabilities.

For 2022–23, the small business income tax gap was approximately 17.4%.

That was higher than the corresponding estimates of 15.9% for 2021–22 and 15.0% for 2020–21.

Why Small Business Compliance Is Difficult to Measure

The small business sector contains a very large number of taxpayers, including sole traders, partnerships, trusts and companies.

Many transactions are not automatically reported by an independent third party.

Cash transactions, private jobs, informal arrangements and business expenses can therefore be harder to verify than salary income reported directly by employers.

This creates more opportunities for both unintentional errors and deliberate under-reporting.

A single omitted transaction may be relatively small, but when similar behaviour occurs across a large number of businesses, the aggregate amount can become substantial.

The Shadow Economy Is a Major Factor

A significant part of the small business gap is associated with shadow economy activity.

This includes cash jobs, unreported sales, hidden business income and overstated deductions.

Shadow economy activity is estimated to account for a large share of the gross small business tax gap.

The issue is not limited to businesses dealing exclusively in cash.

Income can also be omitted where payments arrive through personal bank accounts, online platforms or informal arrangements that are not properly recorded.

The growth of digital payment data has made some of these transactions easier to detect than in previous years.

A Hypothetical Cash-Income Example

Consider a sole-trader tradesperson whose taxable income places additional earnings in the 30% marginal tax bracket.

Assume the person leaves $20,000 of cash jobs out of their return.

At a 30% marginal tax rate, the income tax attributable to that omitted amount would be:

$20,000 × 30% = $6,000.

If the 2% Medicare levy also applies, the combined amount would rise to approximately:

$20,000 × 32% = $6,400.

If the omission is later detected, additional penalties and interest may apply.

The example is simplified and does not account for deductions, offsets or other individual circumstances.

GST Can Also Be Affected

Omitted business income can create more than an income tax issue.

Businesses registered for GST may also under-report GST where taxable sales are left out of activity statements.

For example, cash sales that are not recorded can reduce both reported business income and GST payable.

This means one unreported transaction can contribute to more than one tax-gap category.

Accurate sales records are therefore important for both income tax and GST compliance.

Contractor Pre-Fill Expands the Data Available

Contractor payment reporting has become an increasingly important compliance tool.

Taxable payments annual report data can be used to pre-fill contractor income information for sole traders and individuals in business.

Around 700,000 taxpayers are expected to see contractor payment information pre-filled, covering approximately $21 billion in reported payments.

The industries covered include building and construction, cleaning, courier services, road freight, information technology and security services.

Pre-filled information can make it harder for reported contractor payments to be accidentally or deliberately omitted.

Pre-Fill Does Not Replace Record Keeping

Pre-filled data should not automatically be treated as a complete record of business income.

Contractors can receive payments that are not captured in the reporting system.

Examples can include cash jobs, private clients and income from activities outside the industries covered by mandatory contractor reporting.

Taxpayers still need to check the information against their own records.

Where a pre-filled amount is changed, there should also be a reasonable basis for the adjustment.

Data Matching Covers More Than Contractor Income

Tax administration now receives information from a wide range of external data sources.

Programs can cover areas such as online selling, short-term accommodation, ride-sourcing, motor vehicles, share transactions and high-value assets.

This data can be compared with information reported in tax returns and activity statements.

The purpose is to identify inconsistencies that may indicate omitted income, incorrect deductions or unexplained asset ownership.

Data matching does not automatically mean a taxpayer will be audited.

It is generally used as a risk-identification tool.

Motor Vehicle Data Can Highlight Income Risks

Motor vehicle transaction data is one example of how information can be used for compliance purposes.

Vehicle registration and transfer information can help identify discrepancies between reported taxable income and significant asset purchases.

Higher-value transactions may attract additional attention where they appear inconsistent with a taxpayer's reported financial position.

The information can also assist with GST, fringe benefits tax and luxury car tax compliance depending on the circumstances.

Digital Platforms Create Another Reporting Stream

Online platforms now provide transaction information under the Sharing Economy Reporting Regime.

Ride-sourcing and short-term accommodation transactions have been reportable since 1 July 2023.

Additional categories of platform transactions were brought into the framework from 1 July 2024.

This means income earned through digital platforms is increasingly visible through third-party reporting.

Taxpayers using these platforms still need to ensure the income shown in their own return is complete.

The Tax Gap Is Not the Same as Tax Debt

Tax gap and tax debt measure different issues.

The tax gap generally refers to tax that should have been reported and paid but was not fully collected.

Tax debt refers to liabilities that have already been assessed or reported but remain unpaid.

A business could therefore contribute to the tax gap by failing to report income correctly.

A different business could report all its liabilities accurately but still accumulate tax debt because it cannot pay on time.

Both problems can exist simultaneously.

Why the Difference Matters

The distinction affects how each problem is addressed.

Tax-gap activity often focuses on better reporting, data matching, audits and correcting inaccurate returns.

Tax debt management focuses more on collection, payment arrangements, interest and enforcement.

For small business, both areas are significant because reporting errors and unpaid assessed liabilities can arise from the same underlying pressures, including weak record keeping and cash-flow stress.

Record Keeping Remains Central

Accurate records remain one of the most important protections for small businesses.

Sales, invoices, bank deposits, platform income, contractor receipts and deductible expenses should be recorded consistently.

Cash transactions need the same level of documentation as electronic payments.

Good records make it easier to prepare accurate returns and respond if reported figures are later questioned.

They also reduce the risk that legitimate deductions are lost because there is insufficient evidence.

What to Watch Next

Future tax-gap estimates will show whether the small business share continues to rise or begins to decline.

Contractor pre-fill, platform reporting and expanded data matching should also provide more information about whether better third-party data improves voluntary compliance.

For businesses preparing 2025–26 returns, the central requirement remains straightforward: report all assessable income, including cash and platform earnings, and maintain records supporting deductions.

The increasing volume of information available for data matching means discrepancies between business activity and tax reporting are becoming easier to identify.