Add GST to a price before tax
For a taxable sale at the standard 10% rate, multiply the price before GST by 0.10 to find the GST. Add that tax to the original price. Multiplying the original price by 1.10 gives the same final total.
For example, a $240 service has $24 GST. The customer pays $264. In the calculator, choose Add GST and enter 240. This example assumes the seller is registered and the entire service is taxable.
Remove GST from an inclusive price
Divide the GST-inclusive total by 11 to find its GST component. Subtract that amount from the total to find the price before tax. You can also divide the total by 1.10 to find the unrounded exclusive price.
A $385 total contains $35 GST and $350 before GST. Choose Remove GST and enter 385. Do not take 10% off the total: 10% of $385 is $38.50, which is too much.
Why the divisor is eleven
Think of the price before tax as ten equal parts. Adding 10% adds one more part. The final total now has eleven parts, and one is GST. This explains why the tax is 10% of the exclusive amount but one-eleventh of the inclusive amount.
| Before GST | GST | Total |
|---|---|---|
| $50.00 | $5.00 | $55.00 |
| $250.00 | $25.00 | $275.00 |
| $1,000.00 | $100.00 | $1,100.00 |
Check the transaction before the arithmetic
The calculator does arithmetic; it does not decide whether GST applies. Some sales are GST-free or input-taxed. A business with an ABN is not necessarily registered for GST. Confirm the tax treatment from the invoice, seller and relevant ATO guidance before extracting tax.
Keep the original document alongside your calculated result. For several separate receipts, use the bulk calculator. For a document containing mixed tax treatments, use the invoice maker.
Common questions
What is the GST in $100 including GST?
$9.09, rounded to cents. The amount before GST is $90.91.
Does every sale include GST?
No. Registration and the tax treatment of the sale matter. This calculator assumes a fully taxable sale at 10%.
Official sources
General information only. Examples are illustrative. Check the official guidance for your circumstances. Our editorial approach · Report a correction