A BAS is the form where you tell the ATO how much GST you collected, how much you paid, and a handful of other taxes, all for one chunk of time. One form, one due date, one number at the bottom that you either pay or get back.
Most people meet it the moment they register for GST, and most people quietly dread it. We get why. It looks like admin. But the form itself is the easy part. What makes a BAS painful is everything that has to be true before you open it: clean books, every sale and purchase coded right, payroll reconciled. Get that wrong and the form just faithfully reports the mess.
Who has to lodge one
You lodge a BAS if you are registered for GST. That is the whole rule.
You have to register once your turnover hits $75,000 in a rolling 12 months ($150,000 for not-for-profits). You can register before that voluntarily, and plenty of people do, to claim GST back on startup costs. Either way, from the day you are registered, the BAS is part of your life until you cancel it.
What is actually on it
The core of a BAS is GST: what you charged customers, minus what you paid suppliers. Collect more than you paid and you owe the difference. Pay more than you collected and the ATO owes you.
Then it picks up a few other things depending on your setup. PAYG withholding, the tax you held back from employees’ wages. PAYG instalments, prepayments toward your own income tax. Sometimes FBT instalments or fuel tax credits, though most small businesses never touch those. Figure 1 shows how the pieces land on the one form.
Figure 1. The separate taxes a BAS pulls together, settled as one net amount.
One quick clarification, because it trips people up. If you have PAYG obligations but you are not registered for GST, you might get an IAS instead, an instalment activity statement. Same idea, narrower form: it carries the PAYG labels without the GST ones. Registered for GST means it is a BAS.
How often you lodge
How often comes down mostly to size.
Quarterly is the default, and where most small businesses sit: four statements a year, lined up with the financial-year quarters. Monthly is mandatory once your GST turnover hits $20 million, and some smaller businesses choose it anyway, usually because they are regularly in refund and would rather have the money back than leave it sitting with the ATO for three months. Annual is the quiet option for small voluntary registrants under $75,000: one BAS a year, least admin, but you only see your GST position once, which bites if you have not been setting the money aside.
Figure 2. The three reporting cycles, and what puts you on each.
When it is due
This is the part worth getting onto a calendar, because the ATO does not forget.
Reporting cycle | Period covered | Standard due | If you lodge online yourself | Through a registered agent |
Quarterly Q1 | Jul to Sep | 28 Oct | About 2 weeks later | 25 Nov (2025-26) |
Quarterly Q2 | Oct to Dec | 28 Feb | No extra time | No extra time |
Quarterly Q3 | Jan to Mar | 28 Apr | About 2 weeks later | 26 May (2026) |
Quarterly Q4 | Apr to Jun | 28 Jul | About 2 weeks later | 25 Aug (2026) |
Monthly | One month | 21st of next month | Not available | December month only: 21 Feb |
Annual | Full financial year | 31 Oct, or with your tax return | Not applicable | Not applicable |
Table 1. BAS lodgment cycles and due dates. The agent concession dates shown are the 2025-26 ones and shift slightly when a date lands on a weekend or public holiday. Check the current year against the ATO.
Two things people miss. Lodge your quarterly BAS online yourself and you usually get an extra two weeks past the 28th. Lodge through a registered BAS or tax agent and you get roughly four weeks, for three of the four quarters. The December quarter is the exception either way: it is already pushed out to 28 February, with no further concession on top.
What happens if you are late
Miss the date and two things can happen, and they stack.
First, a failure-to-lodge penalty. The ATO charges one penalty unit for each 28-day period you are late, up to five. A penalty unit is $330 right now, so a small business can cop up to $1,650 on a single statement. We wrote up what a penalty unit is separately. Worth knowing: that penalty can apply even when the BAS comes out at nil or a refund. Late is late.
Second, if you owe money and do not pay, the general interest charge starts running. It compounds daily, sits around 11% a year at the moment, and since 1 July 2025 you can no longer claim it as a deduction. A late payment now costs you the full amount, not a version softened by a tax deduction.
None of this is meant to scare anyone. In practice the ATO is far more forgiving of a business that calls ahead and asks for a deferral than one that simply goes quiet.
How to lodge it
A few ways in. Online through ATO online services, or myGov if you are a sole trader. Straight out of your accounting software, if it is set up for it. Or hand the whole thing to a registered BAS or tax agent, which is also how you unlock those longer due dates.
The mechanical part, pulling the GST totals, filling the right labels, hitting the due date, is exactly the kind of work software should carry. HPLedger runs the books and the BAS and GST side for Australian small business with no subscription. Tax Assistant takes the plain-language version of your position and checks it against current ATO rules, with a registered tax agent signing off before anything is lodged. Either way the point is the same: keep the numbers traceable and let a person sign off, rather than eyeballing it at 11pm on the 28th.
If there is one thing to take from this, it is that the BAS is not the hard part. Keeping books clean enough that the BAS is a five-minute job, that is the hard part, and that is the bit worth your attention.
Technical reference
Legislative basis. Activity statement obligations sit under Division 388 of Schedule 1 to the Taxation Administration Act 1953 (Cth). GST is imposed and reported under A New Tax System (Goods and Services Tax) Act 1999 (Cth); the GST reporting and payment rules are in Division 33. PAYG withholding and PAYG instalments are administered under Schedule 1 to the Taxation Administration Act 1953 (Parts 2-5 and 2-10).
GST registration threshold. Registration is required at a GST turnover of $75,000 ($150,000 for non-profit bodies), or on the day you start a business if you expect to reach it. A business below the threshold may register voluntarily. Once registered, a BAS must be lodged each period regardless of turnover.
Reporting cycles. Quarterly is the default for most small businesses. Monthly is mandatory at a GST turnover of $20 million or more, and may be elected voluntarily by smaller businesses. Annual GST reporting is available to certain voluntarily registered businesses below $75,000.
Quarterly due dates (standard). Q1 (Jul-Sep) 28 October; Q2 (Oct-Dec) 28 February; Q3 (Jan-Mar) 28 April; Q4 (Apr-Jun) 28 July. Self-lodgers who lodge electronically generally receive an automatic two-week deferral for Q1, Q3 and Q4 (not Q2, monthly or annual). Registered agents lodging electronically under the BAS agent lodgment program receive a further concession of about four weeks for Q1, Q3 and Q4. For 2025-26 the agent concession dates are 25 November 2025 (Q1), 26 May 2026 (Q3) and 25 August 2026 (Q4); Q2 has no concession. If a due date falls on a weekend or public holiday, the next business day applies.
Monthly and annual due dates. Monthly statements are due on the 21st day of the following month, with no agent concession except the December statement (due 21 February for eligible business clients). Annual GST returns are due on the due date of the income tax return, or 28 February following the financial year where there is no income tax return obligation.
Failure to lodge on time. The FTL penalty is one penalty unit for each period of 28 days (or part) that a return is overdue, to a maximum of five penalty units. A penalty unit is $330 for infringements on or after 7 November 2024. Small entity maximum is $1,650 (5 units); medium entities (assessable income or current GST turnover of $1 million to under $20 million) apply a multiplier of 2; large entities ($20 million or more) apply a multiplier of 5. FTL can apply even where the statement is nil or a refund.
General interest charge. Unpaid BAS amounts accrue the general interest charge, set quarterly and compounding daily. The annual GIC rate for the April to June 2026 quarter is 10.96%. From 1 July 2025, GIC (and the shortfall interest charge) is no longer tax-deductible.
Lodgment channels. ATO Online services for business; myGov-linked ATO online services for sole traders; Standard Business Reporting enabled accounting software; a registered BAS or tax agent; or by mail. Agent concession due dates require electronic lodgment by the agent and the prior statement lodged electronically, with the client in good standing.
Sources: Taxation Administration Act 1953 (Cth) Sch 1 Div 388; A New Tax System (Goods and Services Tax) Act 1999 (Cth) Div 33; ATO, Due dates for lodging and paying your BAS; ATO, BAS agent lodgment program 2025-26; ATO, GST registration and General interest charge rates. Current to June 2026.
