First quarter BAS for 2026–27: due dates, GST tips and mistakes to avoid

The first quarter of the 2026–27 financial year ended on 30 September 2026. For most small businesses registered for GST, that means the first business activity statement (BAS) of the new year is now due.

Here are the key dates, what goes on your BAS, and the GST mistakes we see most often, so you can lodge accurately and on time.

Q1 BAS due dates for 2026–27

The later agent date applies to both lodging and paying, but only if your agent lodges electronically and you are on their client list before the original due date. If a due date falls on a weekend or public holiday, you can lodge and pay on the next business day.

What goes on your BAS

Depending on your registrations, your BAS can include:

• GST: total sales (G1), GST on sales (1A) and GST credits on purchases (1B)
• PAYG withholding: total wages paid (W1) and the tax withheld from them (W2)
• PAYG instalments: prepayments towards your business or investment income tax
• Other items such as fuel tax credits, fringe benefits tax instalments or wine equalisation tax

Most small businesses with a GST turnover under $10 million use Simpler BAS, which only asks for G1, 1A and 1B for GST.

GST essentials

• You must register for GST once your GST turnover reaches $75,000 ($150,000 for not-for-profits). Taxi and rideshare drivers must register regardless of turnover.
• GST is 10% of the price. On a GST-inclusive amount, the GST is one-eleventh.
• To claim a GST credit you generally need a tax invoice for purchases over $82.50 including GST.
• If you account on a cash basis, you report GST when money is received or paid. On an accrual basis, you report it when you issue or receive an invoice, even if it hasn't been paid yet.

Common GST mistakes to avoid

The ATO pays close attention to GST refund claims and unusual changes from one quarter to the next. These are the errors we see most often:

1. Claiming GST on items that don't include it, such as bank fees, interest, wages, super, most government fees and many basic food items.
2. Claiming the private part of a purchase. If a phone, car or internet plan is 60% for business, only 60% of the GST is claimable.
3. Missing or invalid tax invoices, especially for larger purchases.
4. Counting loans, owner contributions or transfers as sales, which overstates GST on income.
5. Unreconciled accounting software. Duplicated bank feed transactions or wrong tax codes in Xero, MYOB or QuickBooks flow straight into your BAS.
6. Mixing up periods, such as including a July invoice in last year's June quarter or claiming the same invoice twice.

Found an error in an earlier BAS? Many mistakes can be corrected in a later BAS if they are within the ATO's time and value limits. Larger errors may need the earlier BAS to be revised. Ask us before you adjust anything.

Super is no longer a quarterly deadline

Until this year, the super guarantee for July to September was due on 28 October, the same day as many BAS. Since 1 July 2026, Payday Super means employers pay super with each pay run, and it must reach the employee's fund within seven business days. Super isn't reported on your BAS, but check that your payroll is set up for the new timing. Our Payday Super guide explains the rules.

If you can't pay on time

• Lodge on time anyway. Failure-to-lodge penalties are separate from interest on unpaid amounts, and lodging shows the ATO exactly what you owe.
• Interest adds up daily. The ATO's general interest charge is 11.51% a year for the October–December 2026 quarter, and since 1 July 2025 it is no longer tax deductible.
• Ask about a payment plan. Many small businesses can set one up online, or we can arrange it for you.

To make next quarter easier, consider moving the GST you collect into a separate account each week, so the money is there when the BAS is due.

Checklist before you lodge

1. Reconcile every bank and credit card account to 30 September 2026.
2. Check that sales and purchases carry the right GST codes.
3. Make sure you hold tax invoices for purchases over $82.50.
4. Remove the private portion of mixed-use expenses.
5. Match W1 and W2 to your Single Touch Payroll reports.
6. Compare the figures with last quarter and the same quarter last year, and be ready to explain big changes.
7. Lodge by the due date, and pay or arrange a payment plan.

Want us to look after your BAS? As registered tax agents, we can lodge through the agent program, giving you until 25 November 2026 for this quarter. We can also review your bookkeeping so the numbers are right first time. Learn more about our accounting and bookkeeping services, or book a free 15-minute consultation. Consultations are available in English, Punjabi (ਪੰਜਾਬੀ), Hindi (हिंदी), Urdu (اردو) and Gujarati (ગુજરાતી).

This article contains general information only and does not take your personal circumstances into account. Due dates can differ if you have a lodgment deferral or a different reporting cycle. Speak with a registered tax agent before acting.