GST calculator

Add GST to an amount that doesn't include it yet. Type the amount and see the GST and the total, worked out to the cent.

By Book Keeping Pros
Sources checked 15 Oct 2026

Add GST to an amount

Enter the amount before GST. The result updates as you type.

Amount before GST

In dollars and cents, such as 1,250.50

General information only. It works out the figures for the amount you enter and doesn't take your circumstances into account.

Total including GST

Enter an amount

Show working

Enter an amount to see the working.

How it works

GST is 10% of the value of a taxable sale.

The calculator works in whole cents. It multiplies the amount by the rate, rounds the GST to the nearest cent, then adds that GST to the amount to give the total.

Because the total is the amount plus the rounded GST, the figures shown always add up.

Worked example

The GST Act's own example is a car with a value of $20,000. The GST on it is $2,000, so its price including GST is $22,000.

What the result assumes

The amount is for one sale that is fully taxable at the standard rate.
The amount you enter doesn't include GST. For a price that already includes it, use the reverse GST calculator.
The GST is rounded to the nearest cent, with half a cent rounding up, as the ATO sets out for a tax invoice with one taxable sale.
It doesn't cover GST-free or input-taxed sales, or a sale where only part is taxable.
It doesn't apply special valuation rules, such as the margin scheme, or convert foreign currency.

Sources

A New Tax System (Goods and Services Tax) Act 1999
Federal Register of Legislation. Compilation No. 96, compilation date 1 January 2026, released 30 January 2026. Checked 15 October 2026.
Based on content from the Federal Register of Legislation at 15 October 2026. For the latest information on Australian Government legislation please go to https://www.legislation.gov.au. Licence: CC BY 4.0.
How GST works
Australian Taxation Office. Current at 14 September 2026, released 14 September 2026. Checked 14 October 2026.
© Australian Taxation Office for the Commonwealth of Australia Licence: ATO website copyright notice (copy, adapt and distribute, without implying ATO endorsement).
Tax invoices
Australian Taxation Office. Current at 18 September 2026, released 18 September 2026. Checked 15 October 2026.
© Australian Taxation Office for the Commonwealth of Australia Licence: ATO website copyright notice (copy, adapt and distribute, without implying ATO endorsement).

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Calculators

Reverse GST calculator

Questions about this calculator

Something else on your mind? Ask us directly.

What's the difference between GST-exclusive and GST-inclusive?

A GST-exclusive amount is the price before GST is added. A GST-inclusive amount already has the GST in it. This calculator starts from a GST-exclusive amount; the reverse GST calculator starts from a GST-inclusive price.

How is the GST rounded?

To the nearest cent, with exactly half a cent rounding up. The total is the amount plus the rounded GST, so the two figures always add up to the total shown.

Can I use it for an invoice with several items?

It works out one sale at a time. When a tax invoice has more than one taxable sale, the ATO describes two ways to round the GST, across the whole invoice or sale by sale, and they can give different totals.

Does it work for GST-free items?

No. It applies the standard rate to the whole amount, so it isn't right for GST-free or input-taxed sales, or for a sale where only part is taxable.

General information

This calculator applies the GST rate and rounding rule from the GST Act and ATO guidance to one amount. It's general information, not advice about your circumstances, so check how GST applies to your sales before you use the figure. Sources checked 15 October 2026.