The Complete Guide to Quarterly BAS for Sole Traders
If you're a sole trader registered for GST in Australia, you're probably lodging a Business Activity Statement every quarter. And if you're like most sole traders, BAS time is somewhere between mildly stressful and genuinely terrifying.
It doesn't have to be. The BAS is essentially a summary of your GST collected, GST paid, and any PAYG instalment obligations. Once you understand what the key labels mean and where the numbers come from, it's a straightforward process.
What Is a BAS and Who Needs to Lodge One?
The Business Activity Statement is a form submitted to the Australian Taxation Office that reports your tax obligations for the period — primarily GST, but also PAYG instalments (if applicable) and PAYG withholding (if you have employees or contractors who haven't quoted their ABN).
You need to lodge a BAS if you're registered for GST, which is mandatory once your annual turnover hits $75,000. Even if you voluntarily registered below that threshold, you're still on the hook for quarterly lodgement.
Most sole traders lodge quarterly, covering three-month periods aligned to the financial year. Monthly reporting is available if you prefer, but it's more administrative work for the same result.
Understanding the Key BAS Labels
The BAS form has dozens of fields, but for a typical sole trader, you only need to worry about a handful. Here are the ones that matter:
G1 — Total Sales. This is your total income for the quarter, including GST. Every invoice you sent, every payment you received — it all goes here. If you invoiced $33,000 including GST, G1 is $33,000.
1A — GST on Sales. This is the GST component of your G1 figure. For that $33,000 in sales, 1A is $3,000 (the 1/11th GST component).
G11 — Total Purchases. Everything you spent for the business during the quarter, including GST. Software subscriptions, office supplies, subcontractor payments, equipment — the lot.
1B — GST on Purchases. The GST component of your G11 figure. This is what you're claiming back.
Your net GST position is 1A minus 1B. If 1A is $3,000 and 1B is $800, you owe the ATO $2,200. If your purchases were unusually high (maybe you bought a new laptop and some expensive software), 1B could exceed 1A and you'd get a refund.
Step-by-Step: Preparing Your BAS Figures
Step 1: Gather your records. Pull together all invoices issued, all bank statements, and all receipts for the quarter. If you've been tracking expenses consistently throughout the quarter, this is easy. If you haven't, block out an afternoon.
Step 2: Categorise your income. Split your income into GST-applicable and GST-free. Most freelance services are GST-applicable, but some income (like interest or certain government grants) may be GST-free.
Step 3: Categorise your expenses. Same drill — separate expenses with GST from those without. Most business purchases include GST, but some don't (bank fees, government charges, wages if you ever pay them).
Step 4: Calculate your totals. Add up G1, calculate 1A (G1 ÷ 11), add up G11, calculate 1B (G11 ÷ 11). Double-check the arithmetic — calculation errors are the most common reason the ATO sends correction notices.
Step 5: Check for PAYG instalments. If the ATO has notified you of PAYG instalment obligations (a pre-payment toward your income tax), this amount will be pre-filled on your BAS. You can either pay the instalment amount the ATO specifies or calculate your own based on current-year income.
Step 6: Lodge and pay. Submit through the ATO's online services (myGov), your registered tax agent, or compatible accounting software. Pay the net amount by the due date.
Cash vs Accrual: Which Method Are You Using?
This is one of the most important decisions for BAS preparation, and many sole traders don't realise they have a choice.
Cash basis means you report GST when money actually changes hands. You received payment in October? That's Q2 income. You paid for software in September? That's Q1 expense. This is the default for small businesses and the most intuitive method.
Accrual basis means you report GST when you issue or receive an invoice, regardless of when payment happens. You invoiced a client in September but they paid in October? That's Q1 income under accrual.
Most sole traders should use cash basis — it's simpler, matches your bank statements, and avoids reporting income you haven't actually received yet. You can use cash basis if your annual turnover is under $10 million, which covers virtually all sole traders.
BAS Deadlines and Penalties
The quarterly deadlines follow a consistent pattern, due 28 days after the quarter ends:
- Q1 (July–September): Due 28 October
- Q2 (October–December): Due 28 February
- Q3 (January–March): Due 28 April
- Q4 (April–June): Due 28 July
If you lodge through a registered BAS agent, you may get extended deadlines. Electronic lodgement can also provide extra time in some cases.
Late lodgement attracts a Failure to Lodge (FTL) penalty, which starts at one penalty unit for each 28-day period your BAS is overdue, up to a maximum of five penalty units. Late payment incurs the General Interest Charge (GIC), which is calculated daily on the outstanding amount.
The best defence against penalties is simple: don't leave it until the last minute. If you're tracking your transactions throughout the quarter, your BAS figures should be ready days before the deadline, not hours.
Common BAS Mistakes to Avoid
Reporting GST on GST-free items. Not everything has GST. Bank fees, government charges, wages, and some financial services are GST-free. Including these in your GST calculations inflates your 1B claim and can trigger an ATO review.
Claiming GST on private expenses. If you buy a phone that's 60% personal use and 40% business, you can only claim GST credits on the 40% business portion. Claiming the full amount is a common audit trigger.
Forgetting about adjustments. If you claimed a GST credit on something and then used it privately, or if you wrote off a bad debt, you may need to make an adjustment. These are easy to forget but the ATO expects accurate reporting.
Mixing up reporting periods. A payment received on 30 September belongs in Q1. A payment received on 1 October belongs in Q2. Seems obvious, but when you're reconciling bank statements at the end of a quarter, transactions at period boundaries get misclassified constantly.
How FlowFi Makes BAS Effortless
The entire BAS preparation process boils down to one thing: having accurate, categorised records of your income and expenses, with the GST component calculated for each.
FlowFi does this automatically. Every transaction is categorised by AI, GST is calculated based on the category, and your BAS figures update in real time throughout the quarter. When deadline day arrives, you're not scrambling — you're reviewing numbers that have been building themselves all quarter.
Your G1, 1A, G11, and 1B figures are right there in your dashboard, ready to be copied into the ATO portal or sent to your BAS agent. No spreadsheets, no receipt sorting, no last-minute panic.
FlowFi prepares your BAS figures automatically as you go. No more quarterly scramble — just review, lodge, and move on. Try FlowFi free at flowfi.com.au