BAS Guide
BAS & GST Returns Australia — How to Lodge, Due Dates & Tips (2026)
Once you’re registered for GST, the Business Activity Statement becomes part of your calendar. Every quarter (for most businesses), you tell the ATO how much GST you collected, how much you paid, and settle the difference.
It’s not complicated once you’ve done it twice. This guide covers the due dates, the calculation, the cash-vs-accrual choice, and what happens when you’re late — plus a working calculator further down that does the net GST maths for you.
The Basics
What is a Business Activity Statement?
A Business Activity Statement (BAS) is the form GST-registered businesses lodge with the ATO to report and pay GST. Think of it as a running tab with the tax office.
Through the quarter, you collect GST on your sales — that money was never really yours. At the same time, you pay GST on your business purchases — and that money is claimable back. The BAS nets the two against each other: GST collected on sales minus GST credits on purchases equals your net GST payable. Or your refund, if the credits win.
Depending on your setup, the same form may also handle PAYG withholding and PAYG instalments. But GST is the engine of it, and that’s what this page covers.
Frequency
How Often Do You Lodge a BAS?
|
Reporting cycle |
Who it applies to |
|---|---|
|
Quarterly |
Most businesses — the default under $20 million turnover |
|
Monthly |
Compulsory at $20 million+ turnover (optional below) |
|
Annually |
Some voluntary registrations with turnover under $75,000 |
Quarterly is where nearly every small business lands. Monthly suits businesses that prefer smaller, more frequent payments — or that regularly receive refunds and want them faster.
Mark the Calendar
BAS Due Dates 2026–27
|
Quarter |
Period |
Due Date |
Online Extension |
|---|---|---|---|
|
Q1 |
Jul–Sep |
28 October |
+2 weeks |
|
Q2 |
Oct–Dec |
28 February |
No extension (already extended) |
|
Q3 |
Jan–Mar |
28 April |
+2 weeks |
|
Q4 |
Apr–Jun |
28 July |
+2 weeks |
Monthly lodgers: the 21st of the following month. Annual lodgers: 31 October.
A couple of quirks worth knowing. The Q2 deadline is 28 February rather than 28 January — the ATO builds in extra time for the Christmas break — which is why there’s no online extension on top. And lodging through a registered BAS or tax agent generally buys you even later deadlines than the online extension does.
When is my BAS due?
Quarterly BAS is due on the 28th of the month following the quarter end (28 Oct, 28 Feb, 28 Apr, 28 Jul). Monthly BAS is due on the 21st of the following month.
The Calculation
How to Calculate Net GST Payable
Net GST payable equals GST collected on sales minus GST credits on purchases. Two divisions and a subtraction. That’s the whole calculation.
Say your quarter looked like this:
- Quarterly sales (inc GST): $55,000
- GST collected: $55,000 ÷ 11 = $5,000
- Quarterly purchases (inc GST): $22,000
- GST credits: $22,000 ÷ 11 = $2,000
- Net GST payable: $5,000 − $2,000 = $3,000
You’d pay the ATO $3,000 for the quarter. And if the numbers flipped — credits bigger than collected, common in a quarter where you bought a ute or a big piece of equipment — the ATO refunds you the difference instead.
Why divide by 11? Because in a GST-inclusive price, the GST is 1/11 of the total, not 10%. If that’s new to you, our how to calculate GST page walks through it.
What are input tax credits?
GST credits are the GST you’ve paid on business purchases. You claim them on your BAS to reduce the GST you owe. You need a valid tax invoice for purchases over $82.50. There’s a 4-year time limit.
FREE TOOL
BAS Net GST Payable Calculator
Enter your quarter’s totals and get your BAS GST figure instantly. Everything runs in your browser — nothing is stored or sent anywhere.
All calculations happen in your browser. No data is collected.
How do I calculate how much GST I owe the ATO?
Take your total sales (inc GST) and divide by 11 — that's the GST you collected. Then take your total business purchases (inc GST) and divide by 11 — that's your GST credits. Subtract credits from collected. If the result is positive, you owe that amount. If negative, the ATO owes you a refund.
Methods
Cash vs Accrual — Which GST Accounting Method?
|
Feature |
Cash Basis |
Accrual Basis |
|---|---|---|
|
When you report GST |
When money changes hands |
When invoice is issued or received |
|
Best for |
Small businesses under $10M turnover |
Larger businesses |
|
Advantage |
Never pay GST on unpaid invoices |
Matches most accounting software defaults |
|
Availability |
Turnover under $10 million |
Any turnover |
Cash basis: you report GST when money actually moves — when a customer pays you, when you pay a supplier. Available if your turnover is under $10 million. This is the small-business favourite because you never pay GST on an invoice you haven't been paid for.
Accrual basis: you report GST when the invoice is issued or received, regardless of payment. Larger businesses use it, and it matches how most accounting software thinks by default — worth checking your settings match your ATO election.
There's a third path too: the GST instalment method, where the ATO calculates a quarterly amount for you and you square up with one annual return. More on that next.
Set and Forget
The GST Instalment Method
Eligible small businesses can pay a fixed quarterly GST instalment worked out by the ATO — based on your previous year's GST, uplifted by a GDP adjustment factor, which is 5% for 2026–27. Then you lodge one annual GST return to reconcile the instalments against your actual figures.
The appeal is predictability. Four known payments, no quarterly calculations, one reconciliation. The catch is the flip side of the same coin: if your business shrinks, you're paying instalments based on a better year until the annual wash-up refunds you. You can vary the instalment amount if you think it's too high, but vary it too low and interest can apply.
Best suited to stable businesses that value simplicity over precision.
The Stick
What Happens If You Lodge Late?
Miss the deadline and two things can happen.
First, the Failure to Lodge (FTL) penalty. For small entities it's calculated at one penalty unit per 28-day period (or part thereof) the BAS is overdue, capped at 5 penalty units. Penalty units are indexed, so the dollar figure climbs over time.
Second, general interest charge accrues on any unpaid GST from the due date until you pay. The penalty punishes the late form; the interest punishes the late money. They stack.
The practical advice: lodge on time even if you can't pay in full. The ATO is far more flexible about payment plans than about missing lodgements — and lodging on time keeps the FTL penalty off the table entirely.
What happens if I lodge BAS late?
The ATO may charge a Failure to Lodge penalty calculated per 28-day period overdue, up to 5 penalty units. Interest also accrues on unpaid GST.
Practical Tips
Four Habits That Make BAS Painless
Set the GST aside as you go
Open a separate savings account and move roughly 1/11 of each sale into it. Come BAS time, the money's sitting there. The businesses that struggle with BAS are almost always the ones that spent the GST.
Use accounting software
Xero, MYOB, QuickBooks — any of them will track GST per transaction and pre-fill your BAS figures. The subscription costs less than one bookkeeping catastrophe.
Reconcile monthly, not quarterly
Fifteen minutes a month matching transactions beats a lost weekend every quarter. And errors are easier to spot when the transactions are fresh.
Keep every tax invoice over $82.50
No invoice, no credit — that's the rule. Photograph receipts the day you get them and file them digitally. You need a valid tax invoice for purchases over $82.50 to claim input tax credits. Records need to be kept for five years anyway.
Common Questions