Your Business Activity Statement (BAS) is how you report GST — and, if you have them, PAYG withholding and PAYG instalments — to the ATO. Most tradies lodge quarterly. Reconciled and lodged on time it is a 20-minute job; leave it and the penalties start on their own. Here is the whole thing: the labels, the dates (and the agent trick that buys you weeks), the credits you can actually claim, and what late lodgement really costs.
The labels you fill in
Under $10M turnover you can use the simplified BAS, but these are the fields that matter:
| Label | What goes there |
|---|---|
| G1 | Total sales for the quarter, incl GST (labour + materials invoiced) |
| G10 | Capital purchases with GST (tools, machinery, a work vehicle) |
| G11 | Non-capital purchases with GST (materials, fuel, subbies, mobile, accounting) |
| 1A | GST you collected on sales |
| 1B | GST credits on your purchases (from G10 + G11) |
| W1 / W2 | Wages paid / PAYG tax withheld — only if you employ |
| T7 / T8 | Your PAYG income-tax instalment / a variation to it |
| 9 | The net amount — GST + PAYG combined into what you pay or get back |
Net GST is simply 1A minus 1B.
Quarterly due dates
- Q1 (Jul–Sep): 28 October
- Q2 (Oct–Dec): 28 February — the December quarter gets an extra month. This is NOT 28 January (that is the super date); mixing them up is the classic mistake.
- Q3 (Jan–Mar): 28 April
- Q4 (Apr–Jun): 28 July
(Falls on a weekend or public holiday? The next business day.)
The agent extension is worth knowing: lodging through a registered BAS or tax agent generally buys roughly two extra weeks on the September and June quarters and up to four on the December and March quarters. For a tradie juggling cashflow, that breathing room alone can justify an agent.
The GST credits you can actually claim
You can claim the full GST credit on something bought 100% for the business where you hold a valid tax invoice: building materials and consumables, subbie services that include GST, tools used only on site, public-liability and tools insurance, business-only mobile and software, and your accounting/BAS fees.
The apportionment trap — your ute. A dual-cab used on site during the week and for the school run on weekends is dual-purpose, so you claim only the business-use percentage. Worked example: the ute is 70% business per your logbook; you spend $1,100 on fuel including $100 GST → you claim $70, not $100, at G11. Same logic for home-office running costs and a mixed-use mobile.
No credit on: GST-free purchases or anything from a supplier who is not registered; private expenses; and input-taxed acquisitions (some financial services, residential-rent-related costs).
Cash vs accrual
This decides when GST lands on your BAS — and for a tradie on long payment terms it matters a lot (a $22k progress claim can owe GST a quarter before you are paid). It is covered in full in GST for Tradies.
What late lodgement costs
Two separate hits:
Failure-to-Lodge (FTL) penalty — 1 penalty unit for every 28 days (or part) the BAS is late, capped at 5 units. At the current $330 unit that is up to $1,650 per BAS:
- 1–28 days late: ~$330 (1 unit)
- 29–56 days: ~$660 (2 units)
- over 112 days: the $1,650 cap (5 units)
General Interest Charge (GIC) — on any unpaid BAS amount, compounding daily at a variable rate (recently around 11% a year). And since 1 July 2025, GIC is no longer tax-deductible, so it bites harder than it used to.
The rule that saves you money: lodging and paying are separate. Lodge on time even if you cannot pay — that stops the FTL penalty — then set up a payment plan for the amount owing. See Can't Pay the ATO?.
Common mistakes
- Mixing up Q2 BAS (28 Feb) with the super date (28 Jan).
- Claiming 100% GST on a part-private ute — apportion it to the logbook percentage.
- Claiming credits with no tax invoice, or from a non-registered supplier.
- Not lodging because you cannot pay — that adds an FTL penalty on top of the debt.
- Forgetting GIC is now non-deductible — let it run and it costs more than it looks.
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