Discount Calculator
🇦🇺 Australia version
Prices in Australian shops already include GST, so a discount cuts a price that carries tax. This calculator applies each offer to the running price, shows the combined percentage, and separates the final price into its pre-tax part and the GST itself. The rate menu offers GST at 10% or GST-free.
Use Discount Calculator online
Discount Calculator
Stack discounts in the order a till applies them, work backwards from a sale price, convert any multi-buy into a real percentage, and compare pack sizes on unit price.
Price and discounts
Applies to most goods and services.
The tax contained in a GST-inclusive price is price × rate ÷ (1 + rate), taken on the discounted price. Shelf prices here normally include GST; switch it off for a price quoted without tax.
Each discount comes off the price left after the one before it, not off the original. The gap is 6% — $7.2 on this item.
Step by step
| Step | From | Taken off | Leaves |
|---|---|---|---|
| Sale | $120 | −$36 | $84 |
| Extra code | $84 | −$16.8 | $67.2 |
GST contained in the price
Work backwards
Useful for checking a claimed "was" price. Divide by (1 − rate), never multiply by (1 + rate) — that is a different and smaller number.
Australia rules and figures
- GST is 10% of the price of most goods and services in Australia.
- Basic food, most health and education services, and some exports are GST-free.
- Shelf prices include GST, which is why the tool switches Price includes GST on at the start.
- The GST inside a price is one eleventh of it, so a $110.00 price holds $10.00 of GST.
Sources: ATO: GST (checked 2026-11-08)
How the discount calculator works
Discounts are chained, each taken from the previous result. Because GST is included in shelf prices, the tool divides the final price by 1.1 to find the amount before tax, and the rest is GST.
price before GST = final ÷ 1.10; GST = final − price before GST; line total = payable × quantity
- The rate menu holds GST at 10%, which is selected, and a GST-free option at 0%.
- Price includes GST starts on, so a price is read as the one on the ticket.
- Basic food and many health and education supplies are GST-free, so switch the menu for those items.
- The multi-buy tab ranks buy-one-get-one-free at 50%, 3 for 2 at 33.3% and the other deals.
- The unit-price tab divides each pack price by its amount and flags the cheapest per unit.
How to use the discount calculator
- Enter the original price. Type the shelf price, a quantity and a currency symbol of up to three characters.
- Add discounts in order. Each row has a label, a value and a switch between percent and a fixed amount. The numbers show the order they are applied in.
- Set the tax treatment. Enter a rate and say whether the price already includes it. The tax card shows the net price, the tax and the amount payable. Where a country has several rates, a menu above the field lists them.
- Work backwards from a sale price. Enter what you paid and the advertised percentage to see the original price that figure implies.
- Compare multi-buys and pack sizes. Use the deals tab with the price of one item, then the unit-price tab to compare packs on cost per unit.
Example: $250.00 with 15% off, then 10% off, bought twice
Fifteen percent off $250.00 leaves $212.50, and a further 10% leaves $191.25: $58.75 saved, or 23.5% rather than 25%. With GST at 10% included, the price before GST is $173.86 and the GST is $17.39. Two items cost $382.50. Choosing GST-free leaves $191.25 with no tax split.
When to use the discount calculator
- Stacking a clearance tag and a member discount. Add both in the order the shop applies them and read the combined percentage.
- Finding the GST on a receipt amount. Read the GST line from the tax card, which uses the included-price setting.
- Pricing a GST-free item. Pick the GST-free option to see a price with no tax split.
- Comparing multi-buy offers. Open the deals tab and rank the offers by real percentage.
What the discount calculator does not do
- One rate applies to the entire price, so a mixed basket of taxable and GST-free goods needs two runs.
- Quantity multiplies the per-item result, so a basket voucher goes against a quantity of 1.
- Amounts are unrounded in the sums and shown to the cent.
- Unit price makes no conversion between units, so enter packs in the same unit.
- There are no exchange rates, so the symbol changes the label only.
When something else is a better fit
- When you need a general percentage change, use the Percentage Calculator.
- When you want income tax figures for a salary, use the Tax Calculator.
Questions about the discount calculator
Is GST already in Australian prices?
Yes. GST at 10% is included in shelf prices, so a $191.25 final price holds $17.39 of GST and $173.86 before it.
Why is 15% then 10% not 25% off?
The second discount applies to the reduced price. $250.00 becomes $212.50, then $191.25, which is 23.5% off.
Which items are GST-free?
Basic food, most health and education services, and some exports are GST-free. Use the GST-free option in the rate menu for them.
What does the quantity box do?
It multiplies the result for one item. Two items at $191.25 each come to $382.50 payable.
Does a fixed dollar discount change the answer?
Only when it sits beside a percentage, because the order of a percentage and a fixed amount changes the final price.