Business calculators

Australian GST calculator

Check one price or build an itemised breakdown. Mix taxable and non-taxable items, apply a discount, then copy or save your results as PDF.

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By customlogic.com.au

How to use this tool

1. Choose One amount for a quick GST calculation or Multiple items for quantities, descriptions and a mixed-item breakdown.

2. Choose Add GST for prices excluding tax or Remove GST for prices that already include tax. In multiple-item mode, select each item's GST treatment and an optional discount.

3. Calculate to see the price excluding GST, GST amount and total. Check the itemised breakdown, then copy it or use Print / save PDF.

Add GST or remove GST?

Choose Add GST when your starting prices exclude tax. Choose Remove GST when your prices already include tax. One amount assumes a fully taxable sale. Multiple items lets you choose each line's GST treatment. The tool does not determine whether a sale is taxable.

Worked example

A $100 price excluding GST has $10 GST and a $110 total. If a price already includes GST, divide it by 11 to find the GST component: $110 divided by 11 is $10. Subtracting 10% from an inclusive price would give the wrong answer.

Questions and assumptions

Rounding and limits

For up to 50 items, multiply quantity by unit price and round to cents, apply the shared percentage discount and round again, then calculate and round GST for each line. Half cents round up. Displayed line totals add to the summary. Different invoice rounding methods can differ by a few cents. GST-free and input-taxed lines add no GST; credit entitlements and special schemes are not calculated.

Can I save the calculation?

Print / save PDF creates a report on your device with your inputs, item breakdown, totals and assumptions. Choose your browser's PDF destination or print it. This report is not a tax invoice: it does not establish tax treatment or GST credit entitlement. Refreshing clears your inputs, so save a report before leaving.

Sources and further reading

Built and maintained by Custom Logic. Page updated 7 November 2026.