BAS without the panic: due dates, the extension nobody uses, and the five errors we fix most

BAS is the most predictable obligation a business has. It arrives on the same days every year, the amounts are largely knowable in advance, and yet it is the single most common reason a business ends up with an ATO payment plan. The problem is almost never the tax. It is that the work gets done in the last four days of the window.

When quarterly BAS is actually due

For businesses lodging quarterly, the standard dates are:

Quarter	Period	Standard due date
1	July – September	28 October
2	October – December	28 February
3	January – March	28 April
4	April – June	28 July

Quarter 2 already carries a longer window because of the holidays, which is why it sits at 28 February rather than 28 January.

If your GST turnover is $20 million or more you lodge monthly, due on the 21st of the following month. Some businesses elect monthly voluntarily — usually those in a persistent refund position, because monthly lodgement brings the refund forward.

The extension most businesses do not claim

Lodging through a registered tax or BAS agent generally gives you an additional four weeks for quarters 1, 3 and 4. Quarter 2 does not get the concession, because the deadline is already extended.

That extra four weeks is not a trick. It is a standard concession available to any business on an agent's lodgement program — and it is one of the cheapest pieces of breathing room in the tax system. It matters most in October, when Q1 BAS, the previous year's tax return and the September super guarantee payment all land within a fortnight of each other.

Two conditions people miss. You have to be on the agent's lodgement program before the original due date — appointing an agent on 27 October does not retrospectively extend that quarter. And the extension applies to lodgement and payment together, not lodgement alone.

Lodging on time when you cannot pay

These are two separate obligations, and conflating them is expensive.

Lodge on time regardless. Failure to lodge penalties accrue per 28-day period and are calculated on top of whatever you owe. Then deal with the payment separately — the ATO's payment plan options are considerably more accommodating for a business that has lodged and engaged than for one that has gone quiet.

General interest charge accrues on the unpaid balance and is not a small number. If you are heading into a quarter you know you cannot fund, that conversation is worth having in week two of the quarter, not week thirteen.

The five errors that cause most amendments

GST claimed on GST-free purchases. Bank fees, most basic food, residential rent, and many insurance and government charges. Accounting software will happily code a $600 council rates notice as GST-inclusive if nobody tells it otherwise, and the error repeats every quarter until someone catches it.

GST claimed without a valid tax invoice. For purchases over $82.50 including GST, you need a tax invoice showing the supplier's ABN, the words "tax invoice", and the GST amount or a statement that the total includes GST. A bank statement line is not a tax invoice. If the supplier is not registered for GST, there is no GST to claim no matter what the receipt looks like.

Wages and superannuation coded with GST. Neither carries GST. This one usually comes from a manual journal rather than a bank feed, which is exactly why manual journals deserve a second look.

Motor vehicle and asset purchases claimed in full. GST on a car is capped at one eleventh of the car limit, and the input tax credit is reduced by the private-use proportion. Claiming the full GST on a $70,000 vehicle used 50% privately is a large, findable error.

Timing mismatches on cash versus accruals. If you report GST on a cash basis, you claim credits when you pay, not when you are invoiced — and you remit GST when you are paid, not when you invoice. Software defaults to accruals. If your registration says cash and your file says accruals, every quarter is wrong in a way that eventually reconciles but looks alarming in the meantime.

The habit that fixes most of it

Reconcile monthly, not quarterly. The work is identical in total, but done monthly it is three manageable sessions instead of one bad weekend, and errors are found while you still remember the transaction.

Then set aside the GST as it is collected. A separate bank account that receives roughly one eleventh of every deposit is unglamorous and works. Businesses that do this do not have BAS problems; they have a BAS routine.

When it has already gone wrong

Overdue BAS is fixable, and it is more common than most owners assume. The sequence that works:

1. Lodge everything outstanding, even if the numbers need amending later. Stopping the failure-to-lodge clock is the first priority.
2. Get the ATO integrated client account statement and understand exactly what is principal, what is penalty and what is interest.
3. Apply for a payment plan with a realistic instalment, not an optimistic one — a defaulted plan is worse than a modest one.
4. Ask about remission of penalties and interest. It is not automatic, and it is not guaranteed, but a business with a clean prior history and a genuine reason has a reasonable case. It is very rarely granted to a business that has not lodged.

Most of the fear around BAS comes from not knowing the number. Once the books are current, it becomes an ordinary scheduled payment — and the businesses that treat it that way are the ones that never end up on a payment plan at all.

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General information only, current at the time of writing. Due dates, concessions and thresholds change. This is not tax advice and does not consider your circumstances. If your BAS position needs sorting out, book a free consult.