Nobody sets out to donate money to the ATO. And yet, mistake by tiny mistake, plenty of Sydney businesses manage it every single quarter.
BAS mistakes are rarely dramatic. They're small, boring, and repetitive, which is exactly why they're so easy to make four times a year without ever noticing. Here are the five that come up again and again, and what they're quietly costing you.
1. Claiming GST On Things That Don't Have GST On Them
Bank fees, certain insurance premiums, some government charges, and basic groceries (if you're in food retail) are commonly GST-free or input-taxed. Claiming GST credits on them anyway is one of the most common, most avoidable errors on a BAS.
2. Invoices Landing In The Wrong Period
An invoice dated the last week of one quarter but entered in the next throws out your GST figures for both periods. It's a timing mistake, not a big dramatic error, but it adds up and makes your BAS numbers quietly wrong all year.
3. Getting Motor Vehicle And Private Use Wrong
Claiming 100% of a vehicle's running costs when it's also used for the school run or weekend errands is a classic, and one of the easier things for the ATO to query, since it's such a common area of overclaiming.
4. Lodging Straight From The Software Without Checking
Xero and MYOB are excellent tools, but they'll happily generate a BAS from whatever's been entered, including duplicate transactions, miscoded expenses, or that one payment nobody categorised properly in March.
5. Leaving It Until The Deadline Is Basically Yesterday
Rushed BAS lodgements are where most of the above mistakes actually happen. A calm, reconciled BAS prepared a week early looks very different to one assembled the night before it's due.
What These Mistakes Actually Cost You
Beyond simply overpaying or underclaiming, repeated errors increase your odds of a review, and lodging late because the numbers didn't add up can lead to a Failure to Lodge penalty. If that's already happened, the good news is it's usually fixable: see our guide on how ATO penalty remission actually works.
How Mr Figures Helps
Our professionals in the Bookkeeping & BAS service handle reconciliation and BAS lodgement properly the first time, with direct access to your bookkeeper whenever something doesn't look right. And if your situation ever calls for more than bookkeeping alone, our professional network is ready to step in with the right specialist.
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Let's Discuss Your SituationBAS Mistakes: Common Questions
Yes, though it's usually a pattern rather than one error that draws attention. The ATO uses data matching and industry benchmarking to compare your BAS against your tax return and typical industry ratios, so sudden spikes or mismatches get flagged. An isolated small error is normally just corrected.
It depends on the size of the error. Minor mistakes can usually be fixed by adjusting the figures on your next BAS. Larger or older errors generally need a formal revision request with supporting documentation showing what went wrong. Fix it early: the longer it sits, the more it compounds.
You're legally allowed to lodge your own BAS, and many small businesses do. A registered BAS agent earns their fee once transactions get complex enough that coding errors become costly to unwind, and agents get extended lodgement deadlines plus a stronger position if the ATO queries a figure.
Usually a Failure to Lodge penalty for late lodgement, plus general interest charge on amounts paid late. Genuine, first-time or isolated errors can often be reduced or removed through a remission request, particularly if you disclose the mistake yourself before the ATO catches it first.
This article is general information only and doesn't take into account your personal circumstances. It isn't a substitute for advice tailored to your situation. Book a consultation and we'll take a look at your books with you.