Missing a quarterly BAS (Business Activity Statement) deadline is one of the most expensive admin errors an Australian business can make. The ATO applies failure-to-lodge penalties from the day after the due date, and general interest charges start accruing on any unpaid GST or PAYG balance the same day.

The good news: BAS dates are predictable, and if you lodge through a registered tax or BAS agent like Trinity Accounting Practice, you get an automatic extension on three of the four quarters.

This guide lists every quarterly BAS due date for the 2026 calendar year, explains how the tax agent extension works, and covers the two situations where the dates shift.

The Four Quarterly BAS Periods

Australian businesses on quarterly BAS report and pay GST, PAYG withholding, PAYG instalments and other taxes for four three-month periods each financial year:

  • Quarter 1: 1 July – 30 September
  • Quarter 2: 1 October – 31 December
  • Quarter 3: 1 January – 31 March
  • Quarter 4: 1 April – 30 June

The standard ATO rule: your BAS is due 28 days after the end of the quarter. The exception is Q2, which gets an extra month because of the Christmas / New Year shutdown.

2026 Quarterly BAS Due Dates — Standard ATO Dates

If you lodge your own BAS (not through a registered agent), these are your 2026 deadlines:

  • Q2 FY2026 (Oct–Dec 2025) — due 28 February 2026
  • Q3 FY2026 (Jan–Mar 2026) — due 28 April 2026
  • Q4 FY2026 (Apr–Jun 2026) — due 28 July 2026
  • Q1 FY2027 (Jul–Sep 2026) — due 28 October 2026

If the due date falls on a weekend or public holiday, lodgment and payment shift to the next business day.

2026 Quarterly BAS Due Dates — Extended Dates Through a Registered Tax / BAS Agent

If your BAS is prepared and lodged through a registered tax or BAS agent, the ATO grants an automatic four-week concession on Q1, Q3 and Q4. Q2 does not get an additional extension because it already has the Christmas concession built in.

  • Q2 FY2026 (Oct–Dec 2025) — due 28 February 2026 (same as standard)
  • Q3 FY2026 (Jan–Mar 2026) — due 26 May 2026 (extended)
  • Q4 FY2026 (Apr–Jun 2026) — due 25 August 2026 (extended)
  • Q1 FY2027 (Jul–Sep 2026) — due 25 November 2026 (extended)

To qualify for the extension, the BAS must actually be lodged through the agent’s portal — simply being a client of an agent is not enough. The agent also needs to have you registered on their lodgment list before the original due date.

What About Monthly and Annual BAS?

This guide focuses on quarterly BAS, which is what most Sydney small and medium businesses use. For completeness:

  • Monthly BAS is required for businesses with GST turnover of $20 million or more, or by choice. It is due on the 21st of the following month. There is no tax agent extension for monthly lodgers.
  • Annual BAS is available for some small businesses that have voluntarily registered for GST but have turnover under the $75,000 threshold. It is due 31 October (or with your annual tax return).

What Happens If You Miss the Due Date?

Two things start the day after the due date:

  1. Failure to Lodge on Time (FTL) penalty. The ATO charges one penalty unit for each 28-day period (or part thereof) that the BAS is overdue, up to five penalty units. The penalty unit amount is indexed annually. For small businesses (turnover under $1m), the penalty units are typically charged at the base rate; medium and large entities are charged at multiples of the base rate.
  2. General interest charge (GIC) on any unpaid balance, compounding daily. The GIC rate is set each quarter and is usually several percentage points above the cash rate.

If you have a genuine reason for missing the date — illness, system failure, recent bushfire/flood — the ATO will often remit FTL penalties on request, particularly for first-time slips. Don’t ignore it; ask.

The Common BAS Mistakes That Trigger ATO Attention

After 22 years lodging BAS for Sydney businesses, the same handful of issues come up:

  • GST coded wrongly on income. Mixing GST-free, input-taxed and taxable supplies in the wrong codes causes G1 / 1A discrepancies the ATO can spot from a mile away.
  • Claiming GST on items that don’t carry GST. Bank fees, residential rent, most insurance excess payments, ASIC fees — none carry GST.
  • PAYG instalment treated as PAYG withholding (or vice versa). They are different fields and they fund different things.
  • Lodging on time but paying late. Lodgment stops the FTL penalty; it does not stop GIC. If cash flow is tight, lodge on time and contact the ATO to arrange a payment plan.

A Trinity insight from 22 years in practice

The single most common BAS surprise we untangle for new clients is not a missed deadline — it is a BAS that was lodged on autopilot using whatever GST codes Xero defaulted to. If you switched bookkeepers, changed accounting software, or grew past the $75K registration threshold mid-year, get your last four BAS reviewed before you assume the trail is clean.

What This Means for You

  • If you self-lodge: put all four 2026 standard dates in your calendar with a 14-day prep reminder. Diarise the 21st of each month if you also lodge monthly PAYG withholding.
  • If you lodge through a tax agent: confirm in writing you are on their lodgment list before the standard due date of each quarter. The extension is conditional on that registration.
  • If you are routinely late: the fix is almost always upstream — bookkeeping is behind, bank feeds aren’t reconciled, or someone is still chasing supplier invoices. Outsourcing the bookkeeping function usually pays for itself in penalties avoided.

How Trinity Can Help

Trinity Accounting Practice is a registered tax agent based in Beverly Hills, Sydney. We lodge quarterly BAS for hundreds of NSW businesses every quarter — on time, with the proper extension, and with the GST treatment reviewed before lodgment. If you have ever paid an FTL penalty or had a surprise BAS bill, our team can take it off your hands.

Book a 20-minute BAS review with the Trinity team →

General advice only. This article contains general information current as at May 2026 and does not constitute tax, financial or legal advice. It does not take into account your personal circumstances, objectives, or needs. BAS due dates and penalty unit amounts can change — always verify on ato.gov.au. Before acting on any information in this article, you should consider its appropriateness to your situation and seek professional advice from Trinity Accounting Practice or another qualified adviser.


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