Q1 BAS is due 28 October 2026: the 20-minute checklist

The first BAS of the 2026-27 financial year covers 1 July to 30 September 2026 and is due on Wednesday 28 October 2026. That is a normal business day, so there is no weekend extension this quarter. If a registered agent lodges for you, you may have until late November; if you lodge yourself, the 28th is the date.

Here is the whole job as a checklist. If your bookkeeping is reasonably current it is about twenty minutes. If it is not, the first two steps take longer, and everything after them is the same.

Before you start: three facts to confirm

• The period. 1 July to 30 September 2026. If you registered for GST part way through, your statement covers your registration date to 30 September, and the ATO shows the exact period in online services.
• Your basis. Cash (report when money moved) or accruals (report when invoiced). Most sole traders are on cash, and every step below assumes it. Check under your registration details if unsure. See cash vs accruals.
• Whether you have a PAYG instalment. If the ATO entered you into instalments after your last tax return, there will be an amount at T7 (or a rate at T2) on this statement. Look before you start so it is not a surprise at the end.

Step 1: get the three months of statements in (5 minutes)

Export July, August and September from your bank as CSV or PDF, for every business account, and upload them. If you have been uploading monthly, this is a check that all three are there. If you have not, it is the longest step, and still not long: a month of transactions is categorised in a minute or two. Our guide to exporting a bank statement covers each major bank.

Add anything that is not on the statements: cash jobs, income paid into a personal account, expenses paid on a personal card. Those are the lines you will not be reminded about.

Step 2: review the flagged transactions (5 minutes)

AI categorisation gets most lines right and flags the ones it is unsure about. Work through the flagged list and confirm or correct each. The corrections that matter most for the BAS are:

• GST on purchases that have none: bank fees, insurance stamp duty, government charges, wages, most overseas subscriptions. If you claimed GST on an overseas tool that never charged it, fix it now. See GST on overseas subscriptions.
• Private lines in the business account: mark them private so they leave G11 and 1B entirely.
• Mixed-use items: phone, car, internet. Confirm the business percentage is applied, not 100%.
• Platform payouts: if a platform pays you net of its fee, record the gross sale so G1 is right and the fee is claimed.
• Transfers that are not income: money from your personal account, a loan, the GST refund from last quarter.

Step 3: check the big purchases (2 minutes)

Any asset bought in the quarter, such as a laptop, a tool or a vehicle, has GST you can claim in full at the business share on this BAS, regardless of how it is treated for income tax. Make sure you hold the tax invoice for anything over $82.50, and that the GST on a car is capped at one eleventh of the car limit. If you bought equipment in the weeks before you registered, ask your accountant about pre-registration credits before you lodge.

Step 4: read the three labels (3 minutes)

Open the BAS page. On the simpler BAS you are looking at:

• G1, total sales: everything you were paid in the quarter, including GST and including GST-free sales.
• 1A, GST on sales: the GST you collected. One eleventh of G1 if everything was taxable; less if some sales were GST-free.
• 1B, GST on purchases: the GST you can claim on business purchases, at the business share.

Sanity checks: does G1 look like three months of your income? Is 1A roughly G1 divided by 11? Is 1B plausible against what you spent? If a figure looks wrong, it usually traces back to a single miscategorised line, and the transaction list under each label shows which. Our BAS labels guide explains every label if the full form appears instead of the simpler one.

Step 5: the PAYG instalment (1 minute)

If T7 shows a pre-filled amount, accept it unless your income has changed a lot. If you use the rate method, enter the quarter's gross business income at T1 and the form applies your rate. Varying downwards is allowed but carries an interest risk if you underestimate; see PAYG instalments explained.

Step 6: lodge (3 minutes)

Sign in to myGov, open the ATO, go to Activity statements and select the July to September 2026 statement. Enter G1, 1A and 1B, answer the question about whether G1 includes GST, confirm the instalment, review the summary and submit. Save the receipt number with your BAS report. The step-by-step lodgement guide has screenshots-level detail, and the lodge BAS page shows the copy-across.

Step 7: pay (1 minute)

Payment is due the same day. Use the payment reference number on the statement, by BPAY or card, a day or two early so it clears. If 1B exceeded 1A you are due a refund into the account the ATO has on file; check it is current.

If you cannot pay the full amount, lodge anyway and set up a payment plan in online services. Lodging on time avoids the failure-to-lodge penalty, which is separate from interest on the unpaid amount. See missed a BAS if you are already late on an earlier one; catch those up first.

The traps that make it take longer

• Dividing by 10 instead of 11 to extract GST. The GST in a $110 receipt is $10, not $11.
• Reporting net payouts from platforms and agencies as sales.
• Claiming GST on a bank statement line over $82.50 with no tax invoice. Find the invoice or leave it out.
• Forgetting the June quarter refund landed in July and treating it as income.
• Using invoice dates on a cash basis. An invoice dated 29 September and paid 3 October belongs to next quarter.

Also on the calendar

• 28 August 2026 was the TPAR deadline for 2025-26 if you paid contractors in building and construction, cleaning, courier, road freight, IT or security services. If you missed it, lodge it now; see TPAR explained.
• 31 October 2026 is the deadline for your 2025-26 income tax return if you lodge it yourself. It falls on a Saturday, so Monday 2 November. Registered agents have later dates.
• Q2 BAS (October to December) is due 28 February 2027, a Sunday, so Monday 1 March 2027.

Making the next one shorter

Upload October's statement on 1 November, November's on 1 December, December's on 2 January. Review the flagged lines each time. On 1 January the Q2 figures are already there, and the checklist above is steps 4 to 7 only: about eight minutes. FlowFi emails you a digest after each upload, a weekly summary on Monday, and reminders seven and two days before the 28th, so the dates do not depend on your memory.

FlowFi builds your Q1 BAS from three uploaded statements: G1, 1A and 1B prepared, PAYG instalment shown, copy-guide for ATO Online. 14-day free Pro trial, no card. Start at flowfi.com.au