How do I work out the GST for my BAS?

Add up your sales including GST and divide by 11. Do the same for business purchases that included GST. The difference is the net GST you pay (or get back if it's negative).

What is a PAYG instalment?

A prepayment of the income tax on your business income, so you don't get one large bill at tax time. The ATO starts them after you lodge a return with enough business or investment income, and tells you the amount or rate to use.

Do I need to lodge a BAS if I'm not registered for GST?

Only if you have another reason, such as PAYG instalments or withholding from employees' wages. If you're not registered for GST and have neither, you don't lodge a BAS.

Can I get a refund on my BAS?

Yes. If your GST credits are bigger than the GST on your sales, for example in a quarter when you bought equipment, the ATO refunds the difference.

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Sole trader

BAS Calculator

What your quarterly BAS will come to: GST on sales, GST credits and PAYG, and when it's due.

Your BAS for this quarter comes to about $5,000: $2,500 of GST and $2,500 of PAYG.

Sales this quarter

Everything you invoiced, including GST (G1)

Purchases with GST this quarter

Business purchases that had GST in the price, including GST (G10 + G11)

PAYG instalment

The amount on your activity statement (T7). Leave at 0 if you haven't been asked to pay instalments.

Tax withheld from employees' wages

W2. Leave at 0 if you don't employ anyone.

To pay

$5,000

this quarter

Next BAS due

GST on sales (1A)$3,000

GST credits on purchases (1B)-$500

Net GST$2,500

PAYG instalment (5A)$2,500

PAYG withheld (4)$0

Total to pay$5,000

Use these numbers in

Opens the calculator with your figures filled in.

Income tax on about $120,000 a year of sales

Due dates are for lodging yourself. Lodging online usually gives you two extra weeks (not for the October to December quarter), and a tax or BAS agent may get more.

How this is calculated

GST on sales is one-eleventh of your GST-inclusive sales. GST credits are one-eleventh of business purchases that included GST. Net GST is the difference. Add your PAYG instalment and any tax withheld from employees to get the amount to pay. GST-free sales (most basic food, exports) and purchases without GST (bank fees, wages) have no GST to count, so leave them out.

Rates checked September 2026 against the ATO.

What goes on a BAS

A business activity statement (BAS) reports the tax your business owes for a period, usually a quarter. For most sole traders it has three parts:

GST on sales (1A): one-eleventh of what you invoiced, if you're registered for GST.
GST credits (1B): one-eleventh of business purchases that had GST in the price.
PAYG: any PAYG instalment the ATO has asked for (5A), and tax withheld from employees' wages (W2).

When the quarterly BAS is due

If you lodge yourself, quarterly BAS is due on 28 October (July to September), 28 February (October to December), 28 April (January to March) and 28 July (April to June).

Lodging online usually gives you two extra weeks, except for the October to December quarter, which already has an extra month. A registered tax or BAS agent may be able to lodge later.

Frequently asked questions

Sources

General info only. This is a calculator, not financial advice. Rates and thresholds shown are current for FY 2026-27 and simplified for clarity. Always confirm figures with the ATO or a licensed adviser before making decisions.