It is Sunday evening. You have just remembered your BAS is due tomorrow. You open myGov, stare at a form full of labels like G1, G10, 1A, and 1B, and spend the next forty minutes second-guessing every number you enter while quietly wondering if you got it wrong the last three times too.
The Business Activity Statement is one of those things that sounds like it should be straightforward and somehow manages not to be. This guide explains exactly what goes where, how to calculate what you owe, and what happens if you miss the deadline.
The short answer
A BAS is the form GST-registered businesses use to report and pay their GST to the ATO. Most tradies lodge quarterly. You report your total sales at G1, your purchases at G10 and G11, and the difference between the GST you collected and the GST you paid on business expenses is what you owe or get back. Due 28 days after the end of each quarter.
1. Who has to lodge a BAS
Every business registered for GST must lodge a BAS. That means if your annual turnover is over $75,000 - or you registered voluntarily below that threshold - a BAS is mandatory for every lodgement period, even if you earned nothing that quarter.
Most tradies lodge quarterly. Businesses with a turnover over $20 million lodge monthly, which almost certainly does not apply to you. You can also opt into annual lodgement if your GST turnover is under $75,000 and you chose to register voluntarily, but quarterly is the default for anyone above the threshold.
You lodge your BAS through:
- The ATO's online services via myGov - free, direct, and where most sole traders start.
- Accounting software like Xero, MYOB, or QuickBooks - these pre-populate most fields from your invoices and expenses if you keep your records in them.
- Through a registered tax or BAS agent - worth it once the paperwork gets complicated, such as when you start employing people.
2. The fields explained in human language
The BAS form uses codes that seem deliberately designed to cause confusion. Here is what the main ones actually mean:
G1 - Total sales. Every dollar your business invoiced during the quarter, including the GST component. If you invoiced $11,000 including GST, G1 is $11,000. Not $10,000. The full amount.
G2 - Export sales. Sales to overseas customers where no GST applies. Irrelevant for almost every Australian tradie. Leave it blank.
G3 - Other GST-free sales. Sales that are genuinely GST-free under Australian tax law - certain food, medical services, some financial products. Also irrelevant for most trade work. Leave it blank unless your accountant tells you otherwise.
G10 - Capital purchases. Business purchases of assets over $300 - tools, plant, equipment, a vehicle used for work. The full GST-inclusive amount.
G11 - Non-capital purchases. All other business expenses that include GST - materials, fuel, subcontractor invoices, consumables, trade supplies. Again the full GST-inclusive amount.
1A - GST on sales. The ATO calculates this for you based on G1 minus your GST-free sales. It is 1/11th of your taxable sales. This is what you collected on behalf of the ATO from your clients.
1B - GST on purchases. The ATO calculates this based on G10 and G11. It is 1/11th of your GST-inclusive business purchases. This is the GST credits you can claim back.
The net amount you pay or receive back is 1A minus 1B. If you collected more GST than you paid out, you pay the difference. If you paid out more GST on purchases than you collected - common in quarters with big material costs - the ATO refunds the difference.
3. A real example
A plumber invoices $55,000 including GST over the quarter. They spend $16,500 including GST on materials and subcontractors.
- G1: $55,000
- G11: $16,500
- 1A (GST collected): $5,000 (1/11th of $55,000)
- 1B (GST credits): $1,500 (1/11th of $16,500)
- Net GST payable: $3,500
That $3,500 is money the plumber collected from clients on the ATO's behalf across the quarter. The BAS is the mechanism for handing it over.
This is why keeping the GST component of every invoice in a separate account makes life significantly easier. The money was never yours to begin with - you were holding it for the ATO.
4. Due dates - and what happens if you miss them
Quarterly BAS due dates for most tradies:
- Q1 (July - September): due 28 October
- Q2 (October - December): due 28 February
- Q3 (January - March): due 28 April
- Q4 (April - June): due 28 July
Q2 gets an extended deadline because of the Christmas period. The others are a firm 28 days after quarter end.
Missing the deadline triggers a Failure to Lodge (FTL) penalty of one penalty unit - currently $330 - for each 28-day period the BAS remains unodged, up to five penalty units ($1,650) for small businesses. The penalty applies even if your net GST is zero. A nil BAS lodged late still attracts the fine.
If you cannot pay the amount owed, lodge anyway and contact the ATO to arrange a payment plan. Late lodgement and late payment are treated separately. Lodging late while unable to pay is better than not lodging at all - the FTL penalty stacks on top of any interest charges on unpaid amounts.
5. What you can claim back
Every business purchase that includes GST reduces your net liability at 1B. Keep tax invoices for everything:
- Tools and equipment (G10 if over $300, G11 if under)
- Materials, hardware, supplies (G11)
- Fuel for work vehicles (G11)
- Subcontractor invoices where they are GST-registered (G11)
- Work-related phone and internet costs (G11, proportional to business use)
- Safety equipment and PPE (G11)
- Accounting and professional fees (G11)
You need a valid tax invoice for any purchase over $82.50 to claim the GST back. A receipt showing the total amount and the supplier's ABN is usually enough for smaller purchases. For anything significant, make sure you have a proper tax invoice with GST shown separately or a statement that GST is included.
This is where the Invoice Generator pays off on the other side too - every invoice you issue with GST properly recorded makes your G1 calculation straightforward at BAS time instead of a scramble through your inbox.
6. PAYG withholding - if you have employees
If you employ anyone, your BAS also includes PAYG (Pay As You Go) withholding reporting. Two extra fields:
W1 - Total salary, wages, and other payments. The gross amount you paid employees during the quarter.
W2 - Amounts withheld from payments. The tax you withheld from employee wages and remitted to the ATO.
For most tradies who employ apprentices or a labourer, these fields are straightforward if payroll is being tracked properly. If your payroll situation is anything more complex, a BAS agent or accountant is worth the cost.
7. The GST instalment option
If your business income is steady and predictable, the GST instalment method lets you pay a quarterly amount set by the ATO based on your previous year's GST, rather than calculating it from scratch each quarter. You reconcile at the end of the financial year.
For a tradie with variable income - big quarters followed by quiet ones, seasonal work, large material purchases in some quarters - the standard method usually produces a more accurate result and avoids overpaying when income drops.
8. Three habits that make BAS week less painful
Keep a separate GST account. Every invoice you send with GST, move 1/11th of the total into a separate savings account on the day it gets paid. When BAS time comes, the money is sitting there. You are not scrambling to find $4,000 you assumed was yours.
Reconcile monthly, not quarterly. Spending 20 minutes at the end of each month checking your invoices and expenses against your bank statement means BAS week is a 30-minute job, not a three-day panic.
Set a calendar reminder six days out. Not the day before. Six days. Enough time to find a missing invoice, chase a supplier for a tax invoice, or fix something without lodging under pressure.
Get it right, then do it fast
The BAS is not complicated once you understand what the codes mean and what goes where. The tradies who dread it every quarter are almost always the ones who have not set up a simple tracking system - so every lodgement feels like doing it for the first time.
Get the process right once. Then it is 30 minutes, four times a year. For more on what you can claim across your whole tax return, see the guide on tax deductions most tradies miss, and for making sure every invoice that feeds into your BAS is compliant, see how to write a tax invoice as a tradie.
Frequently asked questions
What is the penalty for lodging a BAS late?
The ATO charges a Failure to Lodge penalty of $330 for each 28-day period your BAS is overdue, up to $1,650 for small businesses. It applies even if you owe nothing that quarter. If you cannot pay the amount due, lodge anyway and contact the ATO about a payment plan - late lodgement and late payment are handled separately.
Do I need to lodge a BAS if I had no income for the quarter?
Yes. Once registered for GST, you lodge for every period regardless of turnover. A nil BAS - everything zero - takes two minutes. Missing it because nothing happened still attracts the late lodgement penalty.
What is the GST instalment option and should I use it?
The instalment method lets you pay a fixed quarterly amount set by the ATO based on your previous year's GST, rather than calculating it fresh each quarter. It suits tradies with steady, predictable income. If your turnover varies significantly across quarters, the standard calculation method is usually more accurate and avoids overpaying in slower periods.
Can I claim GST back on tools and materials?
Yes. Tools, materials, fuel, subcontractor invoices - any business purchase that includes GST goes on your BAS at G10 or G11 and reduces your net liability at 1B. Keep tax invoices for everything over $82.50. The GST credits on a big materials quarter can significantly reduce what you owe.