Discount Calculator Australia — Sale Price, % Off & Savings

How to Use This Discount Calculator

Working out a discount is a two-input job — drop in the price and the percentage off.

1. Enter the original price (the pre-discount sticker).
2. Enter the discount percentage offered.
3. The calculator instantly shows the dollar amount saved and the final sale price.
4. Optionally toggle to reverse mode if you only know the sale price and the discount percentage.
5. Compare two deals by running both through the tool and looking at the dollar savings — percentages can mislead on small purchases.

Worked Examples for Australian Shoppers

The formula behind every discount is straightforward: multiply the original price by the discount percentage divided by 100, subtract from the original, and you have the sale price. Below are the discount scenarios Australians run into most often, worked through step-by-step so you can double-check your maths at the checkout.

Example 1 — Kmart 20% off a $150 kettle

Original: $150 · Discount: 20%
Saving = $150 × 0.20 = $30
Sale price = $150 − $30 = $120
Since shelf prices in Australia are GST-inclusive, that's what you pay at the register. Enter $150 and 20% into the calculator to verify.

Example 2 — Woolworths half-price special on $8.50 chocolate

Original: $8.50 · Discount: 50%
Saving = $8.50 × 0.50 = $4.25
Sale price = $4.25
Half-price is the fastest to check mentally — sale price equals savings.

Example 3 — Boxing Day 40% off a $649 David Jones jacket

Original: $649 · Discount: 40%
Saving = $649 × 0.40 = $259.60
Sale price = $649 − $259.60 = $389.40
Quick shortcut: paying 60% of the original, so $649 × 0.60 gives the same answer.

Example 4 — JB Hi-Fi stacked deal: 15% off + $50 store voucher on a $1,299 laptop

Step 1: apply the percentage discount first. $1,299 × 0.15 = $194.85 saved. Sale price = $1,104.15.
Step 2: subtract the flat voucher. $1,104.15 − $50 = $1,054.15. Total saving = $244.85 (18.85% off original).

Example 5 — Reverse: a Target tag reads $22.50, 25% off — what was the original?

Original = $22.50 ÷ (1 − 0.25) = $22.50 ÷ 0.75 = $30
This is useful when you suspect an inflated "was" price during a sale — check the recovered original against what you remember paying last month.

Example 6 — Bunnings B2B ex-GST quote: 12% trade discount on a $2,400 order

Step 1: apply discount. $2,400 × 0.12 = $288 saved. Ex-GST price = $2,112.
Step 2: add 10% GST. $2,112 × 1.10 = $2,323.20 including GST.
Enter $2,400, 12%, and 10 (as the tax) into the calculator to get this in one step.

Discount Types Compared — Which Deal Is Really Better?

Two "30% off" offers can produce different final prices depending on how the discount is structured. This table compares the three most common patterns on a $200 item:

Two takeaways: a single 30% off always beats two 15% off; and "buy N get 1 free" deals only match a headline % off if you actually want N items.

Common Australian Retail Discount Patterns

Boxing Day (26 December)

Australia's biggest sale day of the year — expect 30-70% off across clothing, electronics, and homewares at David Jones, Myer, JB Hi-Fi, The Good Guys, Harvey Norman and smaller boutiques. Always check "was" prices against pre-December pricing; the ACCC monitors misleading "was/now" tags but doesn't catch every inflated original.

EOFY sales (May–June)

End of Financial Year discounts run from mid-May through 30 June — targeting workers who want to claim tax-deductible purchases in the current year. Common on office furniture, business laptops, tools, and vehicle accessories. Business buyers claiming GST credits should enter the ex-GST price and use the tax field to reconstruct the tax-inclusive total.

Click Frenzy and Amazon Prime Day (July / November)

Online-only 24-48 hour flash sales with 15-40% off. Retailers frequently run stacked promo codes — a headline "25% off" often combines with an extra 10% for signed-up members, giving 32.5% effective off (not 35%).

Weekly supermarket half-price specials

Woolworths and Coles cycle 50% off promotions on packaged goods weekly (Wednesday–Tuesday). The advertised "was" price is the shelf price of the previous week, so half-price genuinely means half — no need to reverse-check.

Kmart and Big W clearance markdowns

Rolling clearance stickers of $2, $5, $10, $15 (fixed dollar) rather than percentages. Divide the flat dollar saving by the original to get the effective percentage — a $5 clearance on a $20 item is 25% off.

How This Discount Calculator Works — The Maths

The core formula is:

sale_price = original_price × (1 − discount_percent ÷ 100)
savings = original_price − sale_price
final_with_tax = sale_price × (1 + tax_percent ÷ 100)

For the reverse calculation (recover the original from a sale price and a known percentage):

original_price = sale_price ÷ (1 − discount_percent ÷ 100)

For stacked discounts (two sequential percent-off deals), the effective single-equivalent discount is:

effective_discount = 1 − (1 − d1) × (1 − d2)

where d1 and d2 are the two discounts as decimals. Example: 20% + 10% stacked = 1 − 0.80 × 0.90 = 1 − 0.72 = 0.28 or 28% off. Every calculation runs client-side in JavaScript — the original price and discount you type stay on your device.

Australian Consumer Law — Your Rights on Sale Prices

Under the Australian Consumer Law (ACL, part of the Competition and Consumer Act 2010), it's illegal for a retailer to make a misleading representation about savings — including inflated "was" prices, fake reference prices, and time-limited claims that aren't actually time-limited. The ACCC enforces these rules and has fined major retailers over "was/now" pricing.

A "was $200, now $100" claim is legitimate only if the item was sold at $200 for a reasonable period immediately before the sale. If the "was" price only appeared for two days before a month-long "50% off" event, that's a breach. Use the reverse-calculation feature above to spot-check any suspicious "was" price against your recollection or a price-tracking extension.

Sale terms and conditions must be clear too — "up to 70% off" must actually apply to a meaningful portion of the range, not just one obscure item at the back of the store. If you spot a misleading sale, you can report it to the ACCC.

Related Australian Retail Guides

The discount calculator is the fastest tool for the maths, but a few surrounding topics come up regularly:

• GST on discounted items — GST is calculated on the discounted price, not the original. Use the GST Calculator Australia for the exact 10% split on any tax-inclusive figure.
• Percentage change vs. discount — the maths is symmetric but the framing is different. See the Percentage Calculator for "X is what % of Y" and "% increase/decrease" scenarios.
• Loan and afterpay interest — a "no interest, no payment for 12 months" offer sounds like a discount but can be more expensive than paying now. Compare using the EMI / Loan Calculator.
• Value per hour — deciding if a discount is "worth waiting in line for" is easier when you value your time. Use the Pay Calculator Australia to work out your effective hourly rate first.

Frequently Asked Questions

How do you calculate a 20% discount in Australia?

Multiply the original price by 0.20 to get the dollar saving, then subtract from the original price. Example: a $150 Kmart item at 20% off becomes $150 × 0.20 = $30 saved, giving a sale price of $120. If GST is separately quoted, the 10% GST is applied on the $120 sale price, so the out-the-door price is $132.

How do you calculate 30% off?

Multiply the price by 0.30 for the saving, then subtract. A $200 jacket at 30% off saves $60 and costs $140. Quick trick: 30% off equals paying 70% of the original — so $200 × 0.70 = $140 directly.

How do you calculate 50% off (half price)?

Half price is the simplest — just divide the original price by 2. A $89.95 item on 50% off is $44.98. The dollar saving equals the sale price at exactly 50%.

Is GST added before or after the discount in Australia?

Australian retail prices are almost always GST-inclusive on the shelf, so a 20% off sticker reduces the GST-inclusive price. If a business is quoting ex-GST prices (B2B invoices, wholesale), the discount is applied first and then 10% GST is added to the discounted amount. This calculator supports both — leave the tax field blank for GST-inclusive retail prices, or enter 10 to add GST on top of the discounted figure.

How do stacked discounts work? Is 20% + 10% the same as 30% off?

No — stacked discounts multiply rather than add. Applying 20% off first and then 10% off the reduced price is equivalent to 28% off, not 30%. Formula: 1 − (1 − 0.20)(1 − 0.10) = 1 − 0.72 = 0.28. On a $100 item, single 30% = $70 final, but stacked 20% + 10% = $72 final — a $2 difference. Always calculate the final figure rather than adding the percentages.

How do you reverse-calculate the original price from a sale price?

Divide the sale price by (1 − discount÷100). Example: a Woolworths tag shows $12 with a "25% off" banner. Original price = $12 ÷ (1 − 0.25) = $12 ÷ 0.75 = $16. Useful for spotting inflated "was" prices during sale events.

What is the difference between markup and discount?

Markup adds a percentage to a cost to get a selling price (retailer perspective); discount subtracts a percentage from a selling price to get a sale price (customer perspective). The maths uses the same percentage formula in opposite directions. A 25% markup on a $80 cost gives $100; a 20% discount off $100 gives $80 — same numbers, different labels.

How can I tell if a Boxing Day or EOFY sale is really a good deal?

Use the reverse calculation and compare to the actual historical price. Australian consumer law (ACL section 18) prohibits misleading "was/now" pricing, but inflated "was" prices are still common. Browser extensions like CamelCamelCamel (for Amazon AU) or Honey track price history. If a "70% off" item's "was" price is 40% higher than the average pre-sale price of the last six months, the real discount is closer to 50%.

How do I calculate a bulk-buy discount (e.g., buy 3 for the price of 2)?

The effective discount on a "buy 3 for the price of 2" deal is one-third off, or 33.3%. General formula: pay-for-N of buy-for-M gives a discount of (M − N) ÷ M. So "buy 2 get 1 free" is 33.3% off, "buy 3 get 1 free" is 25% off, and "buy 5 get 2 free" is 28.6% off. Enter that percentage into the calculator to get the effective per-unit cost.