7 Common BAS Mistakes Melbourne Business Owners Make (and How to Fix Them)

Every quarter, thousands of Melbourne small businesses sit down to prepare their Business Activity Statement — and every quarter, the same handful of errors trip people up. Whether you're running a café in Fitzroy, a trades business out of Dandenong, or a consultancy in the CBD, BAS mistakes tend to follow a predictable pattern. The good news: they're almost all avoidable once you know what to look for.

As a Registered BAS Agent working with businesses across Melbourne and Victoria, we see these seven mistakes constantly. Here's what they cost you, and how to fix each one.

Mistake 1: Mixing up cash and accruals GST reporting

Under A New Tax System (Goods and Services Tax) Act 1999, you must report GST on a consistent basis — either cash or accruals — once you've elected a method with the ATO. A common mistake among Melbourne businesses with turnover under $10 million is switching between the two without formally notifying the ATO, usually because invoices get entered in Xero on the date issued while GST is calculated on the date paid.

• The fix: Confirm your reporting basis on the ATO Business Portal or with your BAS Agent, then set your Xero organisation settings to match. Cash-basis businesses should reconcile bank transactions as the source of truth, not invoice dates.

Mistake 2: Claiming GST credits without a valid tax invoice

This is the single most common issue we find during a BAS health check. For any purchase over $82.50 (GST inclusive), you need a valid tax invoice showing the supplier's ABN, the GST amount or a GST-inclusive statement, and the date of issue. Quotes, delivery dockets, and bank statement line items don't count.

• The fix: Use Xero's file attachment feature to snap and store every receipt against the transaction. If a supplier can't produce a proper tax invoice, don't claim the credit — the ATO can and does claw these back on audit.

Mistake 3: Miscoding GST-free and input-taxed items in Xero

Bank fees, interest, residential rent, and some health and education services are GST-free or input-taxed — but they often get coded as "GST on Expenses" by default in Xero because nobody's checked the tax rate on the account. This overstates your GST credits and creates a discrepancy the ATO's data-matching can flag instantly.

• The fix: Review your chart of accounts tax settings annually. Common Melbourne business culprits include bank merchant fees, interstate freight, and government charges like council rates and land tax — all treated differently for GST purposes.

Mistake 4: Lodging late and copping the GIC

The ATO's Failure to Lodge (FTL) penalty applies in units for every 28 days a BAS remains outstanding, and General Interest Charge (GIC) accrues daily on any unpaid balance. For a Melbourne business already juggling quarterly cash flow, this adds an entirely avoidable cost on top of what's owed.

• The fix: Lodging through a Registered BAS Agent under TASA 2009 typically extends your due date by up to four weeks compared with self-lodgement, giving you breathing room to get the numbers right rather than rushing them.

Mistake 5: Getting PAYG withholding out of sync with payroll

PAYG withholding reported on your BAS should match exactly what's been processed through Single Touch Payroll (STP) for the same period. We regularly see discrepancies where a pay run was corrected in Xero Payroll after STP was finalised, but the BAS wasn't updated to reflect the amendment.

• The fix: Reconcile your PAYG withholding payable account against your STP finalisation report before lodging, every single quarter — not just at EOFY.

Mistake 6: Ignoring PAYG instalments until the bill arrives

PAYG instalments are the ATO's way of collecting income tax progressively rather than as one lump sum. Many growing Melbourne businesses — particularly those scaling up from sole trader to company structure — get caught out because the instalment amount was calculated on last year's income and no longer reflects current trading, especially after a strong quarter over Christmas retail or a busy construction season.

• The fix: You can vary your PAYG instalment rate or amount on the BAS itself if your estimated tax for the year has genuinely changed, but be conservative — the ATO can apply penalties if your varied estimate is under 85% of the actual figure.

Mistake 7: Reconciling the bank account after lodging, not before

This is the root cause behind most of the mistakes above. If your bank feed in Xero isn't fully reconciled before you prepare the BAS, you're working from incomplete data — missing transactions, duplicate entries, and unreconciled transfers all distort the GST and PAYG figures.

• The fix: Build reconciliation into your monthly routine, not a quarterly scramble. A clean Xero file with bank rules set up properly means your BAS prep takes an hour, not a weekend.

None of these seven mistakes are complicated on their own. What makes them costly is that they compound — a coding error flows into a lodgement delay, which flows into GIC, which flows into cash flow stress. The businesses we see get BAS right consistently are the ones with clean, monthly-reconciled books and a Registered BAS Agent checking the numbers before they go to the ATO, not after.