How to Lodge a BAS in Australia: A Step-by-Step Guide
How to lodge a BAS in Australia: who must lodge, the quarterly due dates, how to complete each label (G1, 1A, 1B), how to pay, and what the ATO charges if you are late.
By Timothy Hirou GaschereauPublished 10 min read
If you are registered for GST, the BAS is the form you cannot ignore. It looks intimidating the first time, but once you understand a handful of labels and the due dates, lodging one is genuinely straightforward, and for many sole traders it takes 20 minutes a quarter.
Here is the plain-English guide: who has to lodge, when, how to complete each label, how to pay, and what it costs if you are late.
🎯 The essential: A Business Activity Statement (BAS) is how GST-registered businesses report and pay GST (and often PAYG withholding and instalments) to the ATO. If you are registered for GST you must lodge one every period, even a nil BAS with no sales. Most small businesses lodge quarterly, with due dates of 28 October, 28 February, 28 April and 28 July (extended by about four weeks if you lodge online or via an agent, except the February quarter). The core of it is simple: the GST you collected on sales (1A) minus the GST you paid on purchases (1B) is what you pay or get refunded. Lodge late and the ATO charges a failure-to-lodge penalty plus daily interest.
What a BAS is, and who lodges one
A BAS is the single form the ATO uses to collect several obligations at once. If your business is registered for GST you must lodge one; GST registration is mandatory once turnover reaches $75,000 ($150,000 for non-profits), and the obligation still applies if you registered voluntarily below that. Depending on your circumstances a BAS can cover GST collected and paid, PAYG withholding (tax withheld from employees' wages), PAYG instalments (prepaid income tax on your own business income), and a few niche items like fuel tax credits. Even with zero sales and purchases you must lodge a nil BAS. If you are not yet across GST itself, our paying yourself as a sole trader guide explains why GST you collect is not your money.
How often do you lodge?
The ATO assigns your cycle when you register, based on turnover, and you can check it in ATO Online Services. Quarterly is the most common cycle for small businesses (GST turnover under $20 million). Monthly is mandatory at $20 million or more, and some smaller businesses choose it voluntarily to manage cash flow. Annual lodgement is available if you registered voluntarily and turnover is under $75,000, with the annual BAS due 31 October.
Quarterly BAS due dates
| Quarter | Period | Standard due | Online / agent due |
|---|---|---|---|
| Q1 | Jul to Sep | 28 October | 25 November |
| Q2 | Oct to Dec | 28 February | 28 February (no extension) |
| Q3 | Jan to Mar | 28 April | 26 May |
| Q4 | Apr to Jun | 28 July | 25 August |
The October to December quarter gets no extension, so everyone shares the 28 February deadline. If a due date lands on a weekend or public holiday, it rolls to the next business day.
How to lodge: four ways
- ATO Online Services for Business: best for sole traders without software; complete the labels on screen. You get the extended due dates.
- myGov linked to the ATO: lodge from the Business tab, same process as the ATO portal.
- Accounting software (Xero, MYOB, QuickBooks): pulls GST from your transactions, pre-fills the labels, and lodges straight to the ATO. Fewer errors, and recommended once you have real transaction volume.
- A registered BAS or tax agent: they reconcile and lodge for you and give you the extended dates. Worth it if your affairs are complex or you have staff.
Paper is still possible but slow, error-prone and does not attract the extended dates, so avoid it if you can.
Completing your BAS: the key labels
Reconcile your records against your bank statements first, then work through the labels. The heart of it is three numbers:
- G1 (total sales): your gross sales for the period, including GST, across taxable, GST-free and input-taxed sales.
- 1A (GST on sales): the GST you collected. For standard-rated sales this is roughly G1 divided by 11.
- 1B (GST on purchases): the GST you paid on genuine business purchases you hold a valid tax invoice for. Personal expenses do not count, even if paid from the business account.
If you have employees, also complete W1 (wages paid) and W2 (PAYG withheld). If the ATO has you on PAYG instalments, complete T7 (amount) or T8 (rate). Then review every label against your records and lodge before the due date.
Paying, or receiving your refund
If you owe GST, pay by the due date via BPAY, direct debit, card (fees apply) or Australia Post, using the payment reference on your BAS. If you are owed a refund, online lodgements are usually processed within 14 business days to your registered bank account, so keep those details current. One catch worth repeating: lodging on time but paying late still attracts the general interest charge, because lodgement and payment are separate obligations.
What happens if you lodge late
The ATO charges a failure-to-lodge penalty of one penalty unit for every 28 days (or part) overdue, up to five units for a small entity. With a penalty unit at $364 (from 1 July 2026), that is up to $1,820. On top of that, unpaid GST accrues the general interest charge daily (around 11.4% p.a., reviewed quarterly), and since 1 July 2025 that interest is no longer tax-deductible. If you do not lodge at all, the ATO can issue a default assessment that is often higher than your real liability.
If you have a genuine reason (a first slip, hardship, or something outside your control), you can request remission of the penalty through ATO Online Services or by calling the ATO. It is not automatic, but it is available. The simplest protection is good records: keep tax invoices for purchases over $82.50, reconcile before you lodge, and keep records for five years.
Frequently asked questions
Do I have to lodge a BAS if I had no income?
+
Yes. If you are registered for GST you must lodge a nil BAS for every period, even with zero sales and zero purchases. The obligation is triggered by registration, not by activity, and failing to lodge still attracts the failure-to-lodge penalty.
Can I lodge a BAS myself without an accountant?
+
Yes. Sole traders and small businesses can lodge directly through ATO Online Services for Business or via myGov linked to the ATO, and accounting software makes it easier still. You only need a registered BAS or tax agent if you want the extended due dates or prefer to outsource the work.
What is the difference between a BAS agent and a tax agent?
+
Both are registered with the Tax Practitioners Board and can lodge a BAS for you. A BAS agent is registered specifically for BAS services (GST, PAYG withholding, fuel tax credits); a tax agent can do all of that plus income tax returns. You can verify either at tpb.gov.au.
What if I make a mistake on my BAS?
+
You can revise a lodged BAS through ATO Online Services or your agent. For errors under $10,000 net GST impact you can usually correct them on your next BAS rather than lodging a formal amendment. For larger errors, lodge a formal amendment as soon as you spot the issue.
How long does a GST refund take?
+
The ATO typically processes refunds within 14 business days of an online lodgement (paper takes longer). Make sure your bank account details are current in ATO Online Services before you lodge, or the refund will be delayed.
What is a PAYG instalment and does it go on my BAS?
+
A PAYG instalment is a prepayment of your expected income tax for the year. If the ATO has put you on instalments, you generally pay them quarterly via your BAS. The amount or rate is set by the ATO, but you can vary it if your income has changed significantly.
I use Xero or MYOB. Do I still need the ATO portal?
+
No. Accounting software with Standard Business Reporting integration lodges directly to the ATO, so you complete and submit the BAS from within the software. It is still worth keeping your ATO login active for other things, like checking your account balance or updating bank details.
Keep reading
Books worth reading
📚 Recommended reading
The Barefoot Investor
Scott Pape
The Barefoot Investor
Scott Pape
Australia's best-selling money book ever. A simple system for accounts, budgeting, debt and a real emergency fund in one.
Making Money Made Simple
Noel Whittaker
Making Money Made Simple
Noel Whittaker
Australia's classic, comprehensive money guide covering tax, super and investing, updated for today.
On Your Own Two Feet
Helen Baker
On Your Own Two Feet
Helen Baker
An Aussie financial planner's essential guide to money independence for women, covering every life stage from single to separated. Warm, practical and genuinely on your side.
Some links above are affiliate links. If you buy through them, Snowball Invest may earn a small commission at no extra cost to you. We only recommend books we'd suggest anyway.
Sources
- ATO, lodge your BAS
- ATO, BAS due dates
- ATO, general interest charge
- business.gov.au, Business Activity Statements
General information only, not financial, tax or legal advice. It does not take your circumstances into account. Due dates, penalty units and interest rates change, so verify current figures with the ATO or a registered BAS agent before acting.
Was this article useful?
General information only. This article is educational and does not constitute personal financial advice. It does not account for your circumstances. Consider your own situation and seek advice from a licensed adviser before acting. Read our full disclaimer.
Timothy Hirou Gaschereau
Founder of Snowball Invest, not a financial adviser.
I write about what I'm learning myself, because nobody ever taught us how to take control of our own money. It's a skill, not a mystery, and it's never too late to learn it. The best day to start was yesterday, the second best is today.
LinkedIn →Related articles
Sole Trader vs Company in Australia: Which Structure Is Right for You?
Sole trader or company? We break down the tax, liability, cost and admin differences so you can choose the right business structure in Australia.
Sole Trader Tax in Australia: How Much Will You Actually Pay?
There is no special sole trader tax rate in Australia: your profit is taxed at personal marginal rates. Here is how it works, plus GST, deductions and a tax buffer.
How to Reactivate a Cancelled ABN in Australia
Your ABN was cancelled? Here is exactly how to reactivate an ABN in Australia step by step through the Australian Business Register, and what to sort out after.