The Q4 Business Activity Statement covered the April–June quarter. For self-lodgers the deadline was Monday 28 July 2026. Via a registered BAS agent the extended date was 25 August 2026. Both of those dates have passed. The quarter in front of you now is July–September, due 28 October 2026 — that guide is here. The arithmetic below is unchanged, and it is the same arithmetic the BAS calculator uses.
What's in a Q4 BAS
The core sum is straightforward: GST on your sales (1A) minus GST credits on your business purchases (1B) equals your net GST. If you're on PAYG instalments, add the quarter's instalment and that's the total bill.
For a sole trader or small business reporting on a cash basis — the option available to businesses under $10 million aggregated turnover — you enter what actually landed in your account and what you actually paid in the quarter, not what you invoiced or received invoices for.
The arithmetic in two lines
GST in an inclusive price: divide by 11. A customer paid you $110 — the GST inside it is $10. This is the right formula; taking 10% of the inclusive amount overshoots.
GST on an exclusive price: multiply by 10%. You invoiced $1,000 ex-GST — the GST is $100, total $1,100.
▶ Net GST: how the quarter's bill is built
What to leave out
Only enter sales and purchases that actually carry GST. A few things that feel relevant but don't belong:
- Wages — if you have staff, wages go at W1 (tax withheld at W2), not in your sales. There are no GST credits on wages.
- Superannuation — never appears on a BAS; goes directly to your employees' super funds.
- Purchases from unregistered suppliers — no GST was charged, so there's no credit to claim.
- Bank fees and interest — input-taxed, no credit.
- Stamp duty — a state tax with no GST in it.
The weekly set-aside habit for next quarter
The Q4 bill lands because the money was spent instead of parked. The fix isn't discipline — it's a system.
Option A — the bill-based approach: divide your expected quarterly BAS bill by 13 and move that amount into a separate account each week. The bill funds itself before the due date arrives.
Option B — the per-dollar approach: bank 1/11 of every GST-inclusive dollar the day it hits your account. Whatever the quarter ends up doing, the GST side of the bill is funded by definition. You still need to cover the PAYG instalment separately, but there's no forecasting required.
For sole traders not yet on PAYG instalments, a rough 25–30% of net profit set aside for income tax is a reasonable starting point — but your actual rate depends on your total taxable income. The income tax calculator will give you the real number.
What if the cash isn't there on 28 July
Lodge anyway. Lodging and paying are separate obligations, and lodging on time keeps failure-to-lodge penalties off your account. The ATO offers payment plans — interest keeps accruing, but a plan is far cheaper than ignoring the bill.
That interest matters more than it used to. The ATO's general interest charge (GIC) sits at 11.43% p.a. for the July–September 2026 quarter, compounding daily. And since 1 July 2025, GIC is no longer tax-deductible — which makes an unpaid BAS effectively an ~11.4% after-tax loan. Not one most businesses would choose on purpose.
FY 2026–27 due dates — the full picture
| Quarter | Period | Standard due date | Via BAS/tax agent |
|---|---|---|---|
| Q4 | Apr–Jun 2026 | 28 July 2026 | 25 August 2026 |
| Q1 ← next | Jul–Sep 2026 | 28 October 2026 | 25 November 2026 |
| Q2 | Oct–Dec 2026 | 28 February 2027 | No extension past 28 February |
| Q3 | Jan–Mar 2027 | 28 April 2027 | 26 May 2027 |
Two notes worth keeping: lodging online instead of on paper may add around two extra weeks to the standard dates. And monthly lodgers are due on the 21st of the following month. The Q2 quirk — 28 February already includes the standard holiday concession, so an agent can't extend it further. Agent dates for 2026–27 are from the BAS agent lodgment program.
The July–September quarter is the one in front of you now. The 28 October guide covers who it applies to. One thing that guide has to say, because this table does not: super guarantee is no longer on the quarterly BAS clock. From 1 July 2026, Payday Super means the contribution has to reach the fund within seven business days of payday.
Do you need to be registered for GST at all?
GST registration is compulsory once your annual GST turnover reaches $75,000 (or $150,000 for non-profits). Taxi and rideshare drivers are the exception — they must register from their first dollar of income, regardless of turnover. Once you're registered, you charge GST on all taxable sales and can claim input tax credits on business purchases.
Below the threshold, registration is voluntary — but if you register, all the obligations apply, including lodging BAS on time.
For a sole trader or contractor just crossing the $75,000 mark, the contractor hourly rate calculator helps you build the GST obligation — and the tax set-aside — into your pricing from the start.