Discount calculator
Spotted a sale? Pop in the price and the discount and you'll see what you pay and what you save, straight away.
Sale price
Prices in Australia include 10% GST, so the GST part of any price is that price ÷ 11.
Find the original price
What % off is it?
The formulas
sale price = price × (1 − discount ÷ 100)stacked % off = 1 − (1 − d1) × (1 − d2) · original = sale ÷ (1 − d) · % off = (original − sale) ÷ original × 100Worked examples
A $45 top at 40% off: $45 × 0.40 = $18 off, so you pay $27. That $27 includes $2.45 of GST.
A $200 jacket at 40% off with an extra 10% at the checkout: $200 × 0.6 = $120, then $120 × 0.9 = $108. That's 46% off in total, not 50%.
A TV tagged $600 after 25% off was originally $600 ÷ 0.75 = $800. And shoes cut from $160 to $112 are 30% off.
Making the most of the big sales
Black Friday, Click Frenzy, Boxing Day and the end of financial year (EOFY) sales bring the biggest discounts of the year, and plenty of "extra 10% off" codes on top. Those stacked deals are where the maths gets fiddly, so let the calculator do it. A good habit: decide what you're happy to pay first, then check whether the sale price actually gets there.
Common questions
How do I work out 40% off $45?
Multiply $45 by 0.40 to get the saving, $18, then take that off: $45 − $18 = $27. Or just multiply by what's left: $45 × 0.60 = $27.
Is 40% off then an extra 10% off the same as 50% off?
No. The extra 10% comes off the already-reduced price, so it's 1 − (0.6 × 0.9) = 46% off in total, not 50%. On a $100 item you'd pay $54, not $50.
How do I find the original price from a sale price?
Divide the sale price by what's left after the discount. If something is $60 after 25% off, the original was $60 ÷ 0.75 = $80.
How much GST is in a sale price?
Australian shelf prices include GST, so the GST in any price is the price divided by 11. A $27 sale price includes $2.45 of GST. Businesses registered for GST can usually claim that back.
Are sale discounts always a real saving?
Not always. Some stores lift the 'was' price before a sale. It's worth checking the price history or comparing a couple of stores before you buy.