Common BAS Mistakes That Trigger ATO Audits

The ATO doesn't audit at random. It runs your Business Activity Statement figures against data it already holds — from your bank, your customers, your industry benchmarks and your own past lodgements — and looks for things that don't reconcile. Most of what triggers a closer look isn't fraud; it's ordinary mistakes made in a hurry. Here are the ones that come up most often, and how to avoid them.

Claiming GST you're not entitled to

The single most common issue is claiming GST credits on purchases where there's no GST to claim. Not every expense includes GST: many bank fees, most residential rent, wages, government charges and purchases from suppliers who aren't registered for GST are all outside the system. If your bookkeeping applies a standard GST code to everything, you'll systematically over-claim, and that gap shows up when the ATO reconciles your inputs against your suppliers' reporting.

The other version of this is claiming the full GST on expenses that are only partly for business — a vehicle, a phone, a home internet connection. You can only claim the business-use portion, and you need a reasonable basis for the split you've chosen. Guessing generously is exactly the kind of thing benchmarking flags.

Your BAS and your income tax return don't agree

The total sales you report across your quarterly BAS lodgements should reconcile to the income you report at year end. When they don't, the discrepancy is easy for the ATO to see because it holds both. Common causes include coding a sale to the wrong period, treating a GST-free or input-taxed sale as taxable (or the reverse), and forgetting to include cash takings. Reconciling your BAS totals to your accounts before you lodge the annual return catches most of this.

Getting the GST treatment of a transaction wrong

Australia's GST rules have several categories that look similar and behave very differently, and mixing them up is a frequent source of errors:

• Taxable sales carry GST and you claim credits on related purchases.
• GST-free sales (many basic foods, some health and education) carry no GST but you can still claim credits on inputs.
• Input-taxed sales (such as residential rent and most financial supplies) carry no GST and you generally can't claim credits on related costs.

Coding a GST-free or input-taxed sale as taxable — or the reverse — throws out both your liability and your credits. If your business deals in anything near these boundaries, it's worth getting the treatment confirmed once with your accountant and then coding it consistently.

Lodging late, or paying late, repeatedly

An occasional late lodgement isn't a disaster, but a pattern of them changes how the ATO sees you. Consistent lateness, combined with a growing balance, is one of the clearer signals of a business under pressure — and pressure correlates with the kinds of errors and omissions an audit is designed to find. The general interest charge accrues on unpaid amounts, so late payment is also simply expensive. If you genuinely can't pay on time, engaging early and arranging a payment plan is far better than going quiet.

PAYG withholding and super that don't match your payroll

With Single Touch Payroll, the ATO receives your wage and withholding data every pay run. The PAYG withholding you report on your BAS needs to line up with that. A mismatch between what STP shows you paid your employees and what you've reported and remitted is straightforward for the ATO to detect. The same logic increasingly applies to superannuation as payday super rules tighten the link between paying wages and paying the associated super.

How to stay off the radar

None of these require heroics — they require your books to be clean and your lodgements to reconcile. A few durable habits do most of the work:

• Reconcile your accounts to your bank every period, not once a year in a panic.
• Review your GST coding on unusual or large transactions rather than trusting the default code.
• Keep valid tax invoices for what you claim; the ATO can ask for them.
• Check that your BAS totals reconcile to your STP data and, at year end, to your income tax return.
• Lodge and pay on time — or make an arrangement if you can't.

Getting the mechanics right is mostly a systems problem, which is why a well-run finance function pays for itself here. This is general information rather than tax advice — for how these rules apply to your specific circumstances, check the current guidance on the ATO's website or speak with your registered tax or BAS agent.