Percentage Off + GST Calculator

This calculator applies a percentage discount and handles 15 percent GST in a single step, sorting out the order-of-operations confusion that trips people up when a sale price and GST both come into play. It is a common situation in New Zealand retail and trade: a product has a price, there is a discount to apply, and GST is either already included in the ticket price, as it is for consumers, or needs to be added on top, as it is on a GST-exclusive trade or wholesale price. Getting the sequence right matters, because applying GST before or after the discount, or forgetting that a consumer price already contains GST, leads to the wrong number. This tool removes the guesswork. You enter the original price, the discount percentage, and whether the price is GST-inclusive or GST-exclusive, and it returns the final price you pay, the dollar value of the discount, and the GST component. When the price is GST-inclusive, the discount is applied to the ticket price and the GST already inside the discounted price is shown, which is three twenty-thirds of it. When the price is GST-exclusive, the discount is applied first and then 15 percent GST is added to reach the final price. Use it to work out a sale price, to check a discounted invoice, to separate the GST for an expense claim or a return, or to compare a consumer price with a trade quote. The result always reconciles: the final price equals the discounted base plus or including the correct GST. This is an exact calculation, so you can rely on it for pricing, claims and checking receipts.

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$
$80.00
final price
You save$20.00
GST component$10.43
Discounted base$80.00

For consumer (GST-inclusive) prices the discount is applied to the ticket price. For trade (exclusive) prices, GST is added after the discount. An exact calculation.

How it works

The discount comes off the original price first. If the price is GST-inclusive, the final price is that discounted amount and the GST already inside it is three twenty-thirds of the final price. If the price is GST-exclusive, 15 percent GST is added to the discounted base to give the final price.

Worked example

A $100 GST-inclusive item at 20 percent off costs $80, a $20 saving, with about $10.43 of GST already inside that $80. The same $100 as a GST-exclusive price would be discounted to $80, then 15 percent GST added, giving a final price of $92 with $12 of GST on top.

Related calculators

Data sources: the rates and thresholds on this page are maintained against Inland Revenue. Figures are checked twice monthly.

Frequently asked questions

Do I apply the discount or GST first?

Apply the discount first. If the price already includes GST (a consumer price), the discounted figure is your final price and the GST sits inside it. If the price excludes GST (a trade price), add 15 percent GST to the discounted amount to reach the final price.

How do I find the GST inside a price?

For a GST-inclusive price, the GST component is three twenty-thirds of it, which is the same as dividing by 1.15 and subtracting. This calculator shows the GST component automatically so you can itemise it for an expense claim or return.

What is the difference between GST-inclusive and exclusive?

GST-inclusive prices already contain the 15 percent GST, as shown to consumers. GST-exclusive prices, common in trade and wholesale quotes, do not, so 15 percent must be added. Choosing the right mode here ensures the discount and GST are applied correctly.