The September-quarter activity statement is due 28 October — later if you lodge through a registered agent, but confirm that rather than assume it. Whether that date is a five-minute confirmation or a two-day scramble almost never comes down to the form itself. It comes down to the state of your file in the week before. The businesses for whom BAS is a non-event all run the same short reconciliation pass first. Here it is.
The form is easy; the file is the work
A BAS is mostly a summary of numbers your accounting software already holds: GST collected, GST paid, wages and withholding, maybe a PAYG instalment. If the underlying file is clean, generating the statement is a button-press. If it isn't, you're making estimates under time pressure — and estimates are exactly what draw a review letter. So the ritual isn't about the lodgement. It's about making the file true before you look at the summary.
The BAS-week ritual, step by step
Block an hour in the week before the deadline and work through this, in order:
- Reconcile every bank and card account to zero unreconciled. Not "mostly done" — actually matched to the statement. Unreconciled transactions are where phantom GST and missing income hide.
- Sanity-check GST coding on the tricky categories. The recurring offenders: bank fees and interest (input-taxed, no GST), insurance (GST, but often with a stamp-duty component that isn't), government and ASIC fees (usually no GST), overseas software subscriptions (frequently GST-free), and anything with a private-use portion. A handful of miscodings here moves the number more than you'd think.
- Tie wages and withholding back to payroll. The W1 (gross wages) and W2 (PAYG withheld) labels should reconcile to what Single Touch Payroll reported for the quarter. When payroll and the BAS are prepared from different places, this is where gaps open — and it's one of the most automated cross-checks the ATO runs.
- Scan for the one-offs. A large asset purchase, a refund, a loan drawdown, an owner's contribution — the transactions that aren't ordinary trading. Each needs its GST treatment checked deliberately, because they're the ones the software's default rules get wrong.
- Apply the "is this the business I ran?" test. Look at the quarter's GST and income totals and ask whether they match the quarter you actually had. If a normally busy September reads thin, something's uncoded or unreconciled. Your memory is a better auditor than you give it credit for.
The September quarter's own quirks
This is the first BAS of the new financial year, which gives it a few wrinkles the other quarters don't have. The new award rates and payroll changes that started 1 July are now flowing through every pay run, so your W1 should have stepped up — if it hasn't, check that the payroll settings actually updated. Any end-of-year adjustments your accountant made to the June file can spill into July coding. And a reminder on super: under payday super it's no longer a quarterly, BAS-time event but a per-pay-run obligation, so the BAS-week check on super isn't a lodgement — it's confirming each pay run's contributions actually landed inside the window.
Lodge, then note what was messy
The last step of the ritual is the one that compounds: after you lodge, write down the two or three things that were painful this time — the account that never reconciles cleanly, the supplier whose GST is always wrong, the report you had to rebuild. Fix those in the file now, while it's fresh, and next quarter's ritual gets shorter. A clean BAS week isn't luck, and it isn't diligence under pressure; it's the residue of three months of small habits, verified in one hour. Our BAS readiness checker is a quick way to see where your file stands before you start, and the companion piece on building a quarterly rhythm that runs itself covers the habits that make the ritual almost unnecessary.
FAQ
Do I have to lodge by 28 October?
If you lodge the quarterly BAS yourself, generally yes. Lodging through a registered tax or BAS agent usually gives you extra time under the agent's lodgement program — but confirm your specific due date with them rather than assuming the extension applies.
What if I find an error after I've lodged?
Minor GST errors can often be corrected on your next BAS within the ATO's correction limits; larger ones may need a revision. Either way, fixing it promptly and on the record is a very different position from leaving it and hoping.
Can I just hand it all to my bookkeeper?
You can, and for many businesses that's the right call — but the ritual still needs to happen, by someone, before lodgement. Delegating the work isn't the same as skipping the reconciliation.
Sources: Australian Taxation Office, Due dates for lodging and paying your BAS. Current as at 31 July 2026. General information, not advice.
Want to know whether your file is genuinely BAS-ready or just looks it? Our free Business Health Check includes a compliance once-over and takes five minutes.
If this is the problem you are working on, Valont’s Finance hub runs bookkeeping and managed payroll as part of a connected back office, and the back-office cost calculator shows where to start.
About the author
Nick Lucock
Chief Executive Officer, Valont
Nick Lucock is the Chief Executive Officer of Valont and leads its day-to-day operations across Finance, People, Operations and Growth. He runs the team that does the work Valont publishes about: the bookkeeping, BAS and payroll runs, the award interpretation on every pay cycle, the IT and security layer, and the advisor cadence that keeps an owner's back office current. Nick writes the practical side of Valont's library, the processes, systems and tools that keep Australian SMEs compliant and growing, and he is the author of most of the operational articles on the site. He works with owners across construction and trades, health, hospitality and professional services.
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