How do I fill in my first BAS?

You registered for GST, the first quarter flew by, and now there's a BAS sitting in your ATO account with a lot of boxes and a deadline. It's normal to open it, feel your stomach drop, and close it again.

The good news: for most sole traders it's three numbers, plus one more if you pay PAYG instalments. Once you've done one, the next is a 20 minute job.

When it's due

If you report quarterly, each BAS covers three months and is due on the 28th of the month after the quarter ends, except the October to December quarter, which gets an extra month. If the 28th falls on a weekend or public holiday, you have until the next business day.

If you receive and lodge your BAS online yourself, you may get an extra 2 weeks to lodge and pay quarters 1, 3 and 4. For this quarter that would land on Wednesday 11 November 2026. You don't apply for it. If you qualify, the due date in your online account updates automatically, so check what it shows there before you rely on it. The extra time doesn't apply to monthly BAS or to quarterly instalment notices. Registered tax and BAS agents may also have extra time.

The three Simpler BAS labels

Simpler BAS is the default for small businesses with a GST turnover under $10 million. You report:

• G1 Total sales. Everything you sold in the quarter through the business, including GST-free sales. You also tick whether the figure includes GST. Most people report it including GST and tick Yes.
• 1A GST on sales. The GST you charged. If your prices include GST, that's one eleventh of your taxable sales.
• 1B GST on purchases. The GST credits on your business purchases. You don't report the total you spent, only the GST inside it.

Don't put wages from a job, tax refunds, loans, gifts or private sales like your old couch at G1. Round down to whole dollars, no cents, and leave a label blank if it doesn't apply to you.

Cash or accruals: which quarter does it go in?

Your accounting basis decides when a sale or purchase counts.

• Cash basis: you report it in the quarter the money actually moves. An invoice sent in September and paid in October goes on the October to December BAS.
• Accruals (non-cash) basis: you report it in the quarter you issue or receive the invoice, or get paid, whichever comes first.

The cash basis often suits small sole traders because it lines up with the bank account. Use the basis you chose when you registered for GST.

Where PAYG instalments sit

PAYG instalments are prepayments of your income tax, and they go on the same BAS as your GST. The ATO pre-fills which option you're on.

• Amount option: the ATO works out the figure and shows it at T7. You pay that amount, and on a paper form you copy it to 5A.
• Rate option: you enter your instalment income for the quarter at T1 (your business and investment income, without GST), multiply it by the rate shown at T2, and the result goes at T11 and 5A.

Your BAS then adds up what you owe (the GST at 1A plus the instalment at 5A) and takes off your GST credits at 1B. That's your bill for the quarter. If you're not in PAYG instalments, there's simply no instalment section to fill in.

Worked example

Mia's first BAS, July to September 2026

Example only. Mia is a cleaner in Geelong, registered for GST, reporting quarterly on the cash basis with Simpler BAS. All her sales are taxable. She was paid $16,500 including GST this quarter, and paid $4,400 including GST for business purchases that had GST in the price. Her BAS shows a PAYG instalment amount of $900 at T7.

The sums, step by step (Australian dollars)

Step	Sum	Result
G1 Total sales (GST included, tick Yes)	Sales received in the quarter	$16,500
1A GST on sales	$16,500 / 11	$1,500
1B GST on purchases	$4,400 / 11	$400
GST to pay	$1,500 minus $400	$1,100
PAYG instalment (T7, copied to 5A)	Amount shown by the ATO	$900
Total to pay by 28 October 2026	$1,100 + $900	$2,000

Mia lodges $16,500 at G1, $1,500 at 1A and $400 at 1B, and pays $2,000 by 28 October 2026 (or by her later date if her online account shows the 2 week concession).

Her $900 instalment isn't an extra tax. It's credited against her income tax when she lodges her 2026-27 tax return.

Nothing to report? Still lodge

A quiet first quarter is common. Even with nothing to report, you still lodge a nil BAS by the due date. Online, choose Prepare, then Prepare as nil. In many cases you can also phone 13 72 26 at any time to lodge a nil BAS, though some people can't use the phone service, for example if they report GST by instalments or have a pre-filled instalment amount.

Ways to lodge

• Online services for individuals and sole traders, through myGov.
• Online services for business.
• Accounting software that can lodge directly.
• A registered tax or BAS agent.
• Paper, if the ATO has posted you a form.

If you can't pay by the due date, contact the ATO before it passes. General interest charge applies to any amount not paid on time, so a shorter payment plan costs less.

A 20 minute routine for every quarter

1. Total your sales for the quarter, including GST. That's G1.
2. Work out the GST in your taxable sales (divide GST-inclusive taxable sales by 11). That's 1A.
3. Add up the GST on your business purchases from your tax invoices. That's 1B.
4. Check T7 or work out T1 x T2 for your instalment.
5. Lodge, then move the money from your tax and GST account to pay it.

If anything in your business is unusual, like selling an asset, imports, or a mix of private and business purchases, check with the ATO or a registered tax or BAS agent.

Key numbers

The figures this guide uses, 2026-27 financial year

What	Figure and source
Q1 BAS due date	28 October (July, August and September quarter) ATO
Weekend or public holiday rule	Next business day ATO
2 week online concession	Extra 2 weeks for quarterly BAS lodged online, not quarter 2 ATO
Concession quarters	Quarters ending 30 September, 31 March and 30 June, received and lodged online, applied automatically ATO
Simpler BAS default	GST turnover under $10 million ATO
Simpler BAS labels	G1 Total sales, 1A GST on sales, 1B GST on purchases ATO

Free official help

• ATO due dates for lodging and paying your BAS
  The official quarterly and monthly due dates.
• ATO how to lodge your BAS
  Every way to lodge, including nil BAS online or by phone.
• ATO GST reporting methods
  What Simpler BAS is and who it's for.
• ATO Simpler BAS GST bookkeeping guide
  How to sort sales and purchases for G1, 1A and 1B.
• ATO identify your accounting basis
  Cash versus accruals in the ATO's words.
• ATO what if you can't lodge and pay on time
  Payment plans and what to do before the due date.

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Keep reading

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• All sole traders and abn guides

Sources

1. Due dates for lodging and paying your BAS (ATO). https://www.ato.gov.au/businesses-and-organisations/preparing-lodging-and-paying/business-activity-statements-bas/due-dates-for-lodging-and-paying-your-bas, accessed 2026-10-16.
2. GST reporting methods (ATO). https://www.ato.gov.au/businesses-and-organisations/preparing-lodging-and-paying/business-activity-statements-bas/goods-and-services-tax-gst/gst-reporting-methods, accessed 2026-10-16.
3. Choose a method to complete your full BAS (ATO). https://www.ato.gov.au/businesses-and-organisations/gst-excise-and-indirect-taxes/gst/completing-your-bas-for-gst/choose-a-method-to-complete-your-bas, accessed 2026-10-16.
4. Complete your BAS (ATO). https://www.ato.gov.au/businesses-and-organisations/gst-excise-and-indirect-taxes/gst/completing-your-bas-for-gst/complete-your-bas, accessed 2026-10-16.
5. Step 1: Sales, labels G1 to G3 (ATO). https://www.ato.gov.au/businesses-and-organisations/gst-excise-and-indirect-taxes/gst/completing-your-bas-for-gst/complete-your-bas/step-1-sales, accessed 2026-10-16.
6. Step 5: Summary, 1A and 1B (ATO). https://www.ato.gov.au/businesses-and-organisations/gst-excise-and-indirect-taxes/gst/completing-your-bas-for-gst/complete-your-bas/step-5-summary, accessed 2026-10-16.
7. Identify your accounting basis (ATO). https://www.ato.gov.au/businesses-and-organisations/gst-excise-and-indirect-taxes/gst/completing-your-bas-for-gst/identify-your-accounting-basis, accessed 2026-10-16.
8. How to lodge your BAS (ATO). https://www.ato.gov.au/businesses-and-organisations/preparing-lodging-and-paying/business-activity-statements-bas/how-to-lodge-your-bas, accessed 2026-10-16.
9. PAYG instalments, how to complete your activity statement (ATO). https://www.ato.gov.au/forms-and-instructions/payg-instalments-how-to-complete-your-activity-statement, accessed 2026-10-16.
10. Calculate your PAYG instalments (ATO). https://www.ato.gov.au/businesses-and-organisations/income-deductions-and-concessions/payg-instalments/calculate-your-payg-instalments, accessed 2026-10-16.
11. What if you can't lodge and pay on time (ATO). https://www.ato.gov.au/businesses-and-organisations/preparing-lodging-and-paying/business-activity-statements-bas/what-if-you-can-t-lodge-and-pay-on-time, accessed 2026-10-16.
12. Two week lodgment concession, terms and conditions (ATO). https://www.ato.gov.au/general/online-services/in-detail/two-week-lodgment-concession---terms-and-conditions/?page=1, accessed 2026-10-16.
13. Tax invoices (ATO). https://www.ato.gov.au/businesses-and-organisations/gst-excise-and-indirect-taxes/gst/tax-invoices, accessed 2026-10-16.