Business Australia
Discount Calculator Australia
Enter a price and a discount to see the sale price and what you save, including a second discount on top, such as a sale plus a member code. The tool handles GST too, so you can see the GST in a price or the total once GST is added.
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Applied to the already-reduced price.
Sale price
—You save
—
Total discount
—
GST in the sale price
—
Sale price excluding GST
—
Sale price including GST
—
The working
Working with a different rate? Edit the rates this calculator uses
These are the figures we verified on 2026-10-26. Change them to work with a historic period, or with a new rate that has been announced but which we have not published yet.
Australian Taxation Office
How do I calculate a discount?
Multiply the price by the discount as a decimal and subtract it. $250 with 30% off is $175. A further 10% off that price takes it to $157.50, a total saving of $92.50, which is 37% off rather than 40%.
Stacked discounts
Retailers often advertise 'extra 10% off' on top of a sale price. Because the second percentage applies to the lower price, the combined discount is always less than the two added together. 20% then 20% is 36% off, not 40%.
To compare two offers fairly, convert each to a final price rather than comparing percentages.
Discounts and GST
In Australia advertised consumer prices normally include GST, so a 20% discount takes 20% off the GST-inclusive price. For a business buying with GST claimable, the useful figure is the price excluding GST, which the tool shows. A discount does not change the GST rate: it changes the amount it is charged on.
To split GST from a total, use the GST calculator.
How this is calculated
The rule, step by step, so you can check any figure by hand.
sale price = price × (1 − discount ÷ 100)with a second discount: price × (1 − d1 ÷ 100) × (1 − d2 ÷ 100)total discount % = (1 − sale price ÷ original price) × 100GST in a GST-inclusive price = price × GST rate ÷ (100 + GST rate)price including GST = price excluding GST × (1 + GST rate ÷ 100)
Two discounts do not add. 30% off then 10% off is not 40% off: the second is taken from the reduced price, so the total is 37%. The more discounts you stack, the further the total falls short of the sum.
GST is a proportion of the price, so a discount reduces the GST in it by the same proportion. The GST rate used is 10%, editable above if it changes.
A worked example
A $250 item at 30% off, then 10% off that, with GST included in the prices.
- After the first discount$175.00
- After the second$157.50
- Total saving$92.50
- Total discount37%
- GST in the sale price$14.32
$157.50, which is 37% off.
Check whether a quoted '40% off' really is 30% plus 10%.
Working backwards
To find the original price from a sale price, divide by one minus the discount: a $175 sale price after 30% off was $250. To find the discount that gives a target price, divide the sale price by the original and subtract from one.
What it leaves out
Delivery charges, loyalty points and minimum spend conditions are not modelled. Check the terms of each offer.
What this calculator does not do
- Up to two percentage discounts
- GST at the rate you set
- No shipping or fees
- Rounded to the cent
Common questions
How do I take a percentage off a price?
Multiply the price by one minus the discount as a decimal.
Do two discounts add up?
No. The second applies to the reduced price.
Does the discount apply before GST?
In a GST-inclusive price the discount applies to the whole price; the GST shrinks in proportion.
How do I find the original price?
Divide the sale price by one minus the discount.
How much GST is in a price?
Multiply by 10 and divide by 110.
Where these numbers come from
- ATO — GST The 10% GST rate and the registration turnover threshold
Rates last verified 2026-10-26 Every figure Australian Taxation Office sets is re-checked against the source at least once a year, and again whenever a change is announced. Out of date? Tell us and we will fix it.
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