What Is a BAS in Australia? A Plain-English Guide

Most people in Australia meet their first BAS as a form with about thirty boxes on it and no clear instruction about which ones are theirs. For a small business, almost none of them are. Under the ATO’s default reporting method, a business with GST turnover below $10 million fills in three figures and leaves the rest of the GST section blank.

The thing worth knowing before any of the detail: a BAS with nothing on it still has to be lodged. The ATO’s rule is that even if you have nothing to report for the period, you lodge the BAS as nil by the due date. Lodging late runs at one penalty unit for every 28 days, $364 a unit for infringements on or after 1 July 2026, to a maximum of five units, so $1,820 per statement. There is relief where a late statement comes out nil, and it stops working the moment the ATO applies a penalty first.

This guide covers who has to lodge a BAS, what actually goes on it, when it is due, and what it costs to hand over.

What a BAS actually is

A business activity statement is how a GST-registered business reports and pays transaction taxes to the ATO across the year, in between annual tax returns.

The arithmetic at the centre of it is simple. You add up the GST you collected on your sales, subtract the GST you paid on your business purchases, and the difference is either what you owe the ATO or what the ATO refunds you.

You do not apply for a BAS. Register for an ABN and GST and the ATO issues one automatically when it is time to lodge, and emails you 21 days before the due date to say it is available. If the ATO holds an old email address for you, that notice does not arrive and the due date still does.

A BAS is not a tax return. A tax return covers a full financial year, reports your income and deductions, and works out income tax. A BAS covers a month or a quarter, reports transactions, and mostly deals with GST that has already changed hands. Most GST-registered small businesses lodge four BAS and one tax return every year, on separate due dates.

Who has to lodge a BAS

GST registration is the trigger, and the ATO states it without qualification: “If you are a business registered for GST, you need to lodge a business activity statement (BAS).” Not your turnover on its own, not your structure, not simply holding an ABN.

That moves the real question back a step. Registration becomes compulsory once your GST turnover hits $75,000, or $150,000 for a not-for-profit body, and once you are required to register you have 21 days to do it.

Two versions of turnover are tested, and businesses get caught out in both directions. Current GST turnover is this month plus the previous 11. Projected GST turnover is this month plus the next 11. Crossing the threshold on either one generally means registering, but the ATO builds in a release valve: “Even if your current GST turnover is at or above the threshold, you don’t have to register for GST if your projected GST turnover will be less than the threshold.” A single unusually large year does not lock you in forever.

Taxi, limousine and ride-sourcing drivers register regardless of turnover. So do businesses claiming fuel tax credits.

You can also register voluntarily below the threshold, and plenty of low-activity companies do it to claim GST credits on their expenses. Worth going in with your eyes open: voluntary registration brings the BAS obligation with it, four times a year, whether or not there was any activity to report.

What actually goes on the form

A BAS can carry seven different things, and most guides stop after the first three. The ATO’s own list is:

• GST on sales and purchases
• PAYG withholding, the tax you held back from employees’ wages
• PAYG instalments, prepayments towards your own income tax
• FBT instalments, where you pay fringe benefits tax by instalment
• Luxury car tax
• Wine equalisation tax
• Fuel tax credits

Your BAS only carries the components your registrations attract. A sole trader registered for GST with no staff sees the GST section and nothing else. Add one employee and PAYG withholding appears. The remaining four apply to wine producers, importers of cars above the luxury car tax threshold, and businesses claiming fuel tax credits.

Simpler BAS, and why it comes down to three boxes

Simpler BAS is the ATO’s default reporting method for any business with GST turnover under $10 million. Under it the GST section of your BAS comes down to three figures. You also do not have to complete a GST calculation worksheet, and on a paper statement the sections that do not apply can be left blank.

If the left-hand column is not you, those extra labels are not your problem.

The ATO works out which method you are on from the turnover figure in its own records, the one you gave at registration, and rolls it over each financial year. If it has drifted away from reality in either direction, a phone call to 13 28 66 fixes it.

How often you lodge, and when it is due

Your GST turnover decides your reporting cycle, not your preference.

Cycle	Who it applies to	When it is due
Quarterly	GST turnover under $20 million, unless the ATO has told you to report monthly	28 October, 28 February, 28 April, 28 July
Monthly	GST turnover of $20 million or more, or by choice at any size	The 21st of the following month
Annual	Only businesses registered voluntarily, with turnover under $75,000 ($150,000 for not-for-profits)	31 October, or 28 February where no tax return is required

The annual option is the one people ask about and the one that almost never applies. It is available only to businesses that registered voluntarily, which by definition means turnover under $75,000. At $75,000 registration is compulsory, so the businesses most attracted to lodging once a year are the ones excluded from it.

Two things make the quarterly dates less rigid than they look. Lodging online may get you an extra two weeks to lodge and pay a quarterly BAS. The exception the ATO names is quarter 2, and its reasoning is that the 28 February date already carries a one-month extension. Lodging through a registered tax or BAS agent may also buy you time.

The other is the weekend rule. Where a due date falls on a Saturday, Sunday or public holiday, you have until the next business day to lodge and pay. It works the same way for BAS as it does for the income tax return deadline, where the same rule pushed the 2025-26 self-lodged return from 31 October 2026 to 2 November.

Changing cycle is possible but not casual. Ask early in a period and the new cycle can usually start straight away, ask late and it starts at the next quarter or year. Sole traders have to phone or apply in writing rather than doing it online. And you may be knocked back if you have already changed cycle in the last 12 months.

How to lodge your BAS

There are three routes, and the choice affects your deadline.

• Online, through Online services for individuals and sole traders via myGov, Online services for business, or accounting software with Standard Business Reporting built in. Most businesses doing their own BAS use this, and it is where the two-week concession attaches.
• Through a registered tax or BAS agent, who can lodge, vary and pay on your behalf, and may get you extra time.
• By mail, on the paper statement, which the ATO still accepts.

Lodging a nil BAS

The ATO’s position is unambiguous: “Even if you have nothing to report for the period, you still need to lodge your BAS as ‘nil’ by the due date.”

Online, you select Prepare and then Prepare as nil. There is also an automated phone service on 13 72 26, available any time, which takes up to three statements in one call. You need your TFN or ABN and the BAS document ID printed in the top right corner of the statement.

Phone lodgement will not work in four situations: an annual GST return, reporting GST by instalments, varying a statement down to nil, and any statement with a pre-printed amount above zero at labels F1, G21, T2, T7 or 7A.

What lodging late actually costs

The failure to lodge penalty is one penalty unit for each 28 days, or part of 28 days, that a document is overdue, to a maximum of five units. A penalty unit is $364 for infringements on or after 1 July 2026, so the ceiling for a small business is $1,820 per statement. Four late quarters compound into real money quickly.

That base rate applies to individuals and small withholders. Businesses withholding more from wages are multiplied: medium withholders at twice the rate, large withholders at five times.

A warning comes before a penalty. The ATO says it will contact you by phone or in writing before applying a failure to lodge penalty, and that it generally does not apply penalties in isolated cases of late lodgement.

There is also relief where the lodgement produces nothing. The ATO generally will not issue a penalty notice for a late activity statement that results in a refund or a nil result. Two limits sit on that: the relief does not undo a penalty already applied before you lodged, and it does not extend to large withholders. It is a reason to lodge a late nil BAS today rather than a reason to have ignored it, and the same machinery drives what happens if you do not lodge a tax return.

Interest is separate from penalties. The general interest charge runs on unpaid amounts whether or not a penalty is ever applied, which is why the ATO’s advice is to lodge on time even when you cannot pay on time.

Why you might get an instalment notice instead

Some quarters an instalment notice turns up where a BAS should be. Nothing has gone wrong.

The ATO issues a quarterly GST or PAYG instalment notice in place of a BAS when three things are true together: you report and pay quarterly, you pay the instalment amount the ATO has worked out rather than your own figures, and you have no other reporting requirements. The notice shows a GST instalment amount at label G21 and a PAYG instalment amount at T7.

You pay the amount by the due date and keep the notice. Nothing goes back to the ATO. If the figure is clearly wrong for how your year is actually going, you can vary it, and either way the reconciliation happens later at your annual GST return and your tax return.

What it costs to have someone else do it

ReturnTax charges $150 including GST for a quarterly BAS lodgement where the statement is GST only, and $250 where it includes payroll (PAYG withholding), fuel tax credits or instalment variations. Both assume tax-ready records. Outstanding quarters brought up to date are quoted as a fixed fee before any work begins.

The split follows the same line the rest of this guide has drawn. A Simpler BAS with records already in order is three numbers, and plenty of people lodge their own without ever needing help. The case for handing it over is payroll, GST treatment that is not uniform across what you sell, or a stack of quarters you have not filed.