A Business Activity Statement reports GST you collected on sales (1A) minus GST credits on purchases (1B), the PAYG tax you withheld from employees (W2), and any PAYG income-tax instalment (5A). The net of these is what you pay the ATO, or are refunded, each quarter.

When is a BAS due and what happens if I lodge late?

For quarterly reporters, the BAS is generally due on the 28th day after the end of each quarter, with the September quarter extended to 28 October. If you use a registered BAS agent, a further extension typically applies. Lodging late attracts a failure-to-lodge penalty based on the size of your business, and any unpaid amount accrues the general interest charge (GIC) until paid.

Do I need to register for GST before lodging a BAS?

You must register for GST if your turnover reaches or exceeds $75,000 in any 12-month period, or $150,000 for non-profit bodies. Once registered, the ATO will set up a BAS lodgement obligation. Businesses below the threshold can register voluntarily if they wish to claim GST credits, particularly useful in capital-intensive start-up phases.

What is the difference between cash and accruals GST reporting?

Under cash basis accounting, you report GST in the period you receive payment or make payment, regardless of when the invoice was issued. Under accruals basis, you report GST in the period the invoice is issued, even if cash has not yet changed hands. Small businesses with turnover under $10 million can choose either method, but you must apply it consistently once elected.

Australia BAS Estimate Calculator (GST + PAYG)

Estimated quarterly BAS position.

Net BAS amount

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GST on sales (1A)

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GST credits (1B)

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What a Business Activity Statement actually bundles together

A BAS is the single form a registered business lodges with the ATO, usually each quarter, to settle several obligations at once. The big one is GST: the 10 percent you collected on sales, less the GST credits you can claim on the things you bought for the business. On top of that the form sweeps in the PAYG tax you withheld from employees' wages and any PAYG income-tax instalment the ATO has asked you to prepay toward your own tax bill. Add those pieces up and you get one net figure, either a payment to the ATO or, if your credits run ahead, a refund. This estimator does that arithmetic so you can set the cash aside before the lodgement deadline rather than scrambling for it.

Pulling the GST out of a tax-inclusive figure

The part people most often get wrong is the GST itself. Australian prices are quoted GST-inclusive, so the GST is not 10 percent of the total. It is one eleventh. The tool divides each inclusive amount by 11, which is the same as multiplying by 0.10 and dividing by 1.10. Get this backwards and you will overstate the GST on a $110,000 sales figure by nearly $1,000, throwing the whole statement out.

A quarter for a small consultancy

Take the default figures: $110,000 of GST-inclusive sales, $44,000 of GST-inclusive purchases, $9,000 of PAYG withheld from two staff, and a $4,000 PAYG income-tax instalment. The GST on sales is $110,000 divided by 11, or $10,000. GST credits are $44,000 divided by 11, or $4,000. The net GST position is $6,000 payable. Add the wage withholding and the instalment and the statement comes to $19,000 owed for the quarter.

BAS label	Amount

The chart shows how the $19,000 splits across its three sources. Wage withholding, not GST, is often the largest single line for a business with a payroll.

Who lodges quarterly, and a trap to avoid

Most small businesses report and pay GST quarterly once their turnover passes the $75,000 registration threshold. Larger businesses, broadly those with turnover of $20 million or more, lodge monthly. The common cash-flow trap is treating the GST you collect as your money. It is not. The $10,000 of GST on sales is the ATO's, held by you for the quarter, and spending it leaves a hole when the BAS falls due. A clean habit is to move the GST component of each sale into a separate account as it arrives. This tool is built for the owner-operator or bookkeeper who wants a fast sanity check on the quarter before opening the official form in the ATO Business Portal.

A word on which accounting method you are on

Smaller businesses can report GST on a cash basis, counting it only when money actually changes hands, while others must use accruals and report on the invoice date. The difference matters at quarter end if you have issued large invoices that have not yet been paid. This estimator does not distinguish the two, so enter the sales and purchases that match the method your business is registered for.

Frequently asked

Can a BAS produce a refund?

Yes. If your GST credits exceed the GST you collected, for example in a quarter where you bought major equipment, the net GST is negative and the ATO refunds it, assuming there is no PAYG withholding or instalment to offset. Capital-heavy startups frequently sit in refund territory in their early quarters.

Are wages themselves reported on the BAS?

The gross wages and the tax withheld are reported, but the wage cost is not a GST credit because wages do not carry GST. Only the PAYG amount you withheld appears as an amount you owe. Super contributions are not on the BAS at all; they are paid separately to employees' funds.

What if I get the estimate wrong on the actual form?

You can correct most GST errors on a later BAS within the ATO's correction limits rather than amending the original. Still, lodging and paying on time matters more than perfection, because the general interest charge and failure-to-lodge penalties apply to late statements regardless of the amount.

Frequently asked questions

What goes on a BAS?: A Business Activity Statement reports GST you collected on sales (1A) minus GST credits on purchases (1B), the PAYG tax you withheld from employees (W2), and any PAYG income-tax instalment (5A). The net of these is what you pay the ATO, or are refunded, each quarter.
When is a BAS due and what happens if I lodge late?: For quarterly reporters, the BAS is generally due on the 28th day after the end of each quarter, with the September quarter extended to 28 October. If you use a registered BAS agent, a further extension typically applies. Lodging late attracts a failure-to-lodge penalty based on the size of your business, and any unpaid amount accrues the general interest charge (GIC) until paid.
Do I need to register for GST before lodging a BAS?: You must register for GST if your turnover reaches or exceeds $75,000 in any 12-month period, or $150,000 for non-profit bodies. Once registered, the ATO will set up a BAS lodgement obligation. Businesses below the threshold can register voluntarily if they wish to claim GST credits, particularly useful in capital-intensive start-up phases.
What is the difference between cash and accruals GST reporting?: Under cash basis accounting, you report GST in the period you receive payment or make payment, regardless of when the invoice was issued. Under accruals basis, you report GST in the period the invoice is issued, even if cash has not yet changed hands. Small businesses with turnover under $10 million can choose either method, but you must apply it consistently once elected.

Related calculators

GST

GST on a price.

PAYG Instalment

Income-tax instalment.

Sources

ATO — Individual Income Tax Rates 2026-27, Australian Taxation Office

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