Discount Calculator
🇳🇿 New Zealand version
New Zealand prices include GST at 15%, so any discount you stack lands on a tax-inclusive figure. This calculator removes each offer in order, shows the true combined saving, and divides the final price into the part before GST and the GST. It also ranks multi-buy offers and compares pack sizes.
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
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.
New Zealand rules and figures
- GST in New Zealand is 15%.
- Shelf prices include GST, so the tool starts with Price includes GST switched on.
- The GST inside a price is 15/115 of it, so a $115.00 price holds $15.00 of GST.
- New Zealand has one GST rate in this tool, so the rate menu has a single entry.
Sources: Inland Revenue: GST (checked 2026-11-08)
How the discount calculator works
Each discount comes off the running price, as a percentage or a fixed amount. With GST included, the amount before tax is the final price divided by 1.15, and the remainder is GST.
before GST = final ÷ 1.15; GST = final × 15 ÷ 115
- The menu has a single option, Standard rate at 15%, and Price includes GST starts on.
- The starting example is 120 with 30% then 20% off, which the tool reports as 44%.
- A fixed amount is capped at what remains, and zero or blank discount rows are skipped.
- The Work backwards box takes what you paid and an advertised percentage.
- The unit-price tab shows the cheapest pack and how much dearer the others are.
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: $300.00 with 20% off, then 10% off
After 20% the $300.00 price is $240.00; the extra 10% brings it to $216.00, which saves $84.00 (28%, where 30% might be expected). With GST at 15% included, the amount before GST is $187.83 and the GST is $28.17. Working backwards, paying $216.00 after an advertised 28% off implies an original of $300.00.
When to use the discount calculator
- Adding a sale and a loyalty code. Enter both, in order, and read the combined percentage.
- Separating GST for a business expense. Read the GST line from the tax card for a tax-inclusive receipt.
- Testing a stated discount. Use Work backwards to see the original implied by what you paid.
- Choosing a pack size. Enter prices and amounts on the unit tab and see the cheapest per unit.
What the discount calculator does not do
- Only one GST rate is offered, and a zero-rated supply needs the rate typed in by hand.
- Quantity multiplies the item result, so basket-wide vouchers use a quantity of 1.
- The sums are unrounded, with two decimals displayed.
- No unit conversion happens on the unit-price tab.
- No exchange rate is applied to the symbol.
When something else is a better fit
- When you want a plain percentage change, use the Percentage Calculator.
- When you are working on income tax, use the Tax Calculator.
Questions about the discount calculator
Does a New Zealand price include GST?
Yes, GST at 15% is included. In a $216.00 price, $28.17 is GST and $187.83 is the amount before it.
Why are two discounts of 20% and 10% only 28%?
The 10% applies to $240.00, not $300.00. The final price is $216.00, a saving of $84.00.
How do I find a price before the discount?
Divide what you paid by one minus the percentage. $216.00 at 28% off comes from $300.00.
Can I turn GST off?
Yes. Switch Price includes GST off for a price quoted without tax, and the tool adds GST on top.
What if a bundle says 3 for 2?
The deals tab converts it to 33.3% off, which beats a second item at half price at 25%.