AUS/NZ GST CALCULATOR
Add it, strip it, or work backwards from the GST itself — for New Zealand and Australia.
This is based on Australian GST at 10% and New Zealand GST at 15%.
How to use this calculator
If a price includes GST, this calculator will tell you how much.
If a price excludes GST, this calculator will tell you how much GST to add.
If you have the GST portion, this calculator will work out both the GST inclusive and GST exclusive price for you.
Simply choose your country, enter your figure in the appropriate row, and let the calculator do its thing!
A worked example
New Zealand's GST is 15%, and it works two ways depending on what you're doing.
Adding GST to a price is easy: $100 plus 15% is $115. But pulling GST out of a price that already includes it trips people up. If something costs $115 including GST, the GST portion isn't $17.25 (that's 15% of the total, which is wrong). It's $15 - because the GST was added to $100, not to $115.
The shortcut: to find the GST inside a GST-inclusive price, divide by 23 and multiply by 3.
Australia's GST is much simpler - it's 10%, so you just divide by 11.
If you don't like maths, don't worry, the calculator does it for you, both directions.
Quick note: New Zealand's GST has sat at 15% since 2010, so the rate itself is about as stable as tax gets - the "divide by 23, times 3" trick isn't going anywhere. The $60,000 registration threshold and the finer rules can still change, so check ird.govt.nz if you're in business.
What most people get wrong about GST
The classic error is taking 15% off a GST-inclusive price to find the GST. It overstates it every time, because the 15% was added to the original price, not the final one. To go backwards, you divide the inclusive price by 1.15 to get the original, or by 23 and times 3 to get the GST portion directly.
If you're in business, the other thing to know is the $60,000 threshold. Once your turnover crosses $60,000 in a 12-month period, GST registration stops being optional - you have to register, add 15% to your prices, and pass it on to IRD. Plenty of growing side hustles blow past this without realising and get a nasty catch-up bill.
And a few things are treated differently - exports and some financial services are "zero-rated" or exempt - so if you're doing anything beyond straightforward local sales, it's worth checking exactly how GST applies to your situation.
This calculator and page are general information only and not financial advice. Everyone's circumstances will vary - always do your own research and consult your own financial professionals before making decisions.