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BAS Calculator Australia

Free quarterly BAS calculator for Australian businesses. Estimate GST collected, GST credits, and total BAS payable including optional PAYG instalments.

How the BAS GST calculation works

Your quarterly BAS GST obligation is the difference between GST you collected on sales and GST you paid on business purchases.

The formula

GST collected = Total GST-inclusive sales ÷ 11
GST credits = Total GST-inclusive purchases ÷ 11
Net GST payable = GST collected − GST credits
Total BAS payable = Net GST + PAYG instalment (if applicable)

If your GST credits exceed GST collected, the ATO will refund the difference.

What to include in your BAS

Sales (1A on the BAS form)

Include all GST-inclusive income from taxable sales during the quarter. This covers goods sold, services rendered, and other business income that attracts GST.

Purchases (1B on the BAS form)

Include all GST-inclusive business purchases where you can claim a GST credit. This includes:

Stock and raw materials
Operating expenses (rent, utilities, subscriptions)
Equipment and asset purchases
Professional services (accounting, legal)
Employee expense reimbursements (where GST was charged)

Items to exclude

Do not include GST-free sales (exports, basic food, medical services), input-taxed supplies (financial services, residential rent), or purchases where no tax invoice was provided.

Tips for accurate BAS lodgement

Engage a registered BAS agent or accountant to prepare and lodge on your behalf
Reconcile your accounts before lodging
Ensure all supplier invoices are valid tax invoices
Check that employee expenses have receipts with ABN and GST amounts
Review any large or unusual transactions
Keep records for at least five years

Estimate your quarterly BAS

Total sales (inc. GST) ($)

Total purchases (inc. GST) ($)

PAYG instalment amount ($)

$30,000 GST collected

$10,000 GST paid (credits)

$20,000 net GST

$20,000 total BAS payable

Q1 (Jul–Sep 2025) due 28 Oct 2025

Frequently asked questions

What is a BAS in Australia?

A Business Activity Statement (BAS) is a form submitted to the ATO to report and pay several tax obligations including GST, PAYG instalments, PAYG withholding, and other taxes. Most small businesses lodge BAS quarterly.

How is the GST component of a BAS calculated?

The GST payable on your BAS is: GST collected on sales minus GST credits on purchases. GST collected is one-eleventh of your GST-inclusive sales. GST credits are one-eleventh of your GST-inclusive business purchases.

When are quarterly BAS due?

Quarterly BAS due dates are: Q1 (Jul-Sep) due 28 October, Q2 (Oct-Dec) due 28 February, Q3 (Jan-Mar) due 28 April, Q4 (Apr-Jun) due 28 July. If you lodge electronically, you may get an additional two weeks.

What is a PAYG instalment?

Pay As You Go (PAYG) instalments are regular prepayments of your expected income tax liability. The ATO calculates an instalment amount or rate based on your most recent tax return. These are reported on your BAS alongside GST.

What happens if I lodge my BAS late?

Late lodgement can result in a Failure to Lodge (FTL) penalty of $313 per 28-day period (up to a maximum of 5 periods). Late payment incurs the General Interest Charge (GIC), which is updated quarterly by the ATO.

Methodology and disclaimer

This calculator estimates your quarterly BAS GST obligation using the standard ATO BAS reporting method. GST collected = total GST-inclusive sales ÷ 11. GST credits = total GST-inclusive purchases ÷ 11. Net GST = GST collected minus GST credits. Total BAS payable = Net GST plus any PAYG instalment amount.

This simplified calculation assumes all sales and purchases include GST at 10%. It does not account for GST-free supplies, input-taxed supplies, adjustments, wine equalisation tax, luxury car tax, fuel tax credits, or PAYG withholding. Your actual BAS may include additional labels and obligations.

This tool provides estimates only and does not constitute financial, tax, or legal advice. Always consult a registered tax agent or BAS agent for your specific circumstances. Rates are current as at 1 July 2025.

BAS-ready books, every quarter

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