Free NZ GST calculator. Add or extract 15% GST on quotes, invoices, and supplier prices.
This tool adds NZ GST to a price, or pulls the GST back out of a price that already includes it. Two fields, one rate, and one trap that costs builders real money on quotes.
Adding GST is the easy direction: multiply by 0.15 and add it on. An amount of 100 dollars plus GST is 115 dollars.
Going the other way is where it goes wrong. Take 15% off 115 dollars and you get 17.25 dollars — but the GST inside 115 dollars is 15 dollars, not 17.25. To pull GST out you divide by 1.15, because the 15% was calculated on the smaller, GST-exclusive number in the first place.
The shortcut worth memorising is that the GST inside a GST-inclusive figure is three twenty-thirds of it. On 115 dollars: 115 times 3, divided by 23, is 15. That is the same arithmetic as dividing by 1.15, in a form you can do on a phone at a merchant counter.
Most trade suppliers quote a builder GST-exclusive, and most homeowners read any number you give them as the total they will pay. A quote that does not say which one it is will eventually be read the wrong way, and the 15% comes out of your margin rather than the client's pocket.
The safe habit is to state it on the document — GST-exclusive or GST-inclusive, in words, next to the number. CostMate estimates carry that through to the client-facing quote so the client sees which basis they are reading.
The two directions are separate tabs here on purpose, because they are separate questions and mixing them up is the whole problem.
This is arithmetic, not tax advice. Confirm your GST obligations with Inland Revenue or your accountant, and state on every quote whether the figure includes GST.