By Joshua Occhino, Co-founder, Ezyiah
Short answer: ATO scrutiny of a BAS is rarely random. It's usually triggered when figures don't line up with other data the ATO holds, or with what similar businesses report. Examples are BAS sales that don't reconcile with the income tax return, PAYG withholding that doesn't match Single Touch Payroll, figures well outside your industry's small business benchmarks, or large swings between quarters with no explanation. Most of these can be caught with a short check before lodgement.
How does the ATO decide which BAS to look at?
The ATO uses data matching to compare what you report with information from third parties and with your other lodgements. It also publishes small business benchmarks by industry and says it uses them as one of the tools to identify businesses that may be avoiding their tax obligations. So a review usually starts with a mismatch, not a person picking a file at random.
What usually triggers a BAS review or letter?
- Income that doesn't reconcile. Sales on the BAS that don't line up with income in the tax return for the same period.
- PAYG withholding mismatches. W2 on the BAS that doesn't match what was reported through Single Touch Payroll. See STP and BAS don't match: how to find and fix the gap.
- Out-of-range ratios. Cost of sales, labour or margins well outside the benchmark for the industry, with no business reason on file.
- Unexplained swings. A big jump or drop in GST on sales or purchases from one quarter to the next.
- Repeated amendments. Revising the same periods over and over suggests the underlying process isn't fixed.
- High-risk categories. Fuel tax credits, GST on imports and private-use adjustments claimed inconsistently or unusually high for the turnover. See fuel tax credits and BAS errors.
Which BAS errors cause the most trouble?
- Wrong GST codes. Claiming GST credits on wages or super (which carry no GST), mishandling overseas software subscriptions, and treating GST-free sales as taxable or the reverse.
- The wrong accounting method. Businesses with aggregated turnover under $10 million can choose to account for GST on a cash basis. If the software is set to accruals while the business is registered for cash, every BAS is on the wrong basis.
- PAYG withholding gaps. Bonuses or back pay run outside the normal pay cycle, or contractor payments where no ABN was quoted and withholding was missed.
- Duplicates and period errors. Duplicates from CSV imports and transactions dated into the wrong quarter.
What should you check before lodging?
- BAS sales reconcile to the accounting records and, at year end, to the tax return.
- W1 and W2 match the STP reports for the period.
- The GST accounting method in the software matches the ATO registration.
- Any large movement against the prior quarter has a note explaining it.
- GST on wages, super, bank fees and overseas subscriptions is coded correctly.
What if you find an error after lodging?
Fix it quickly. Many GST errors can be corrected on a later BAS within the ATO's time and value limits. Where there's a shortfall, base penalties are 25% (failure to take reasonable care), 50% (recklessness) or 75% (intentional disregard). A voluntary disclosure made before the ATO tells you about an examination reduces the base penalty by 80%, and a shortfall under $1,000 may attract no penalty. See what voluntary BAS disclosure does to your penalty.
How Ezyiah helps
Ezyiah is an AI bookkeeper with its own ledger. It reconciles live bank feeds with AI and builds the BAS, Extended BAS, P&L and Balance Sheet from the same books, so quarter-on-quarter movements and coding problems are visible before the due date. AI Memory keeps coding consistent across quarters, and receipts and bills are matched to the transactions they support. Your accountant reviews and approves the BAS before lodgement.
See how it works for accounting firms and business owners.
Frequently asked questions
Does a letter from the ATO mean I'm being audited?
Not necessarily. Many letters come from automated data matching and ask you to check or explain a figure. Respond promptly and with records.
Are ATO audits random?
Rarely. Reviews are usually triggered by data matching, benchmarks or risk patterns.
Will amending a BAS trigger an audit?
An occasional correction is normal. Repeated amendments to the same periods can draw attention, so fix the cause, not just the number.
