Sales Tax Calculator
A sales tax calculator lets you add a tax rate to a price or pull the tax back out of a figure that already includes it. You enter the amount and the rate, then choose whether you are adding tax to a net figure or extracting tax from a gross figure, and the tool returns the tax portion alongside the total or net amount. In New Zealand the usual sales tax is GST, which sits at 15 percent, but the calculator accepts any rate so it works for other jurisdictions or for modelling a change. Adding tax takes a net amount and grows it by the rate, while extracting tax takes a tax inclusive amount and works backwards to find the tax already baked in, which is the part people most often get wrong. The common trap is taking 15 percent of a GST inclusive total, when you should divide by 1.15 to find the net and then take the difference. This tool handles that division for you, so your invoices, quotes, and bookkeeping stay accurate. It suits small business owners, contractors, and anyone reconciling receipts or preparing a return. A few tips keep things clean. Decide up front whether your prices are quoted including or excluding tax and stay consistent across a document, since mixing the two is a frequent source of errors. Keep tax aside as you receive it rather than treating it as income, because it is money you are collecting on behalf of the tax office. When in doubt, check the official rate that applied on the transaction date. All figures are shown in New Zealand dollars and the result is an estimate to help you check your own workings.
Add: tax = net x rate. Extract: net = gross / (1 + rate); tax = gross - net. Estimate only, not financial or tax advice.
How it works
In add mode the amount is treated as a net figure and the tax is the amount multiplied by the rate, with the total being net plus tax. In extract mode the amount is treated as tax inclusive, so the net is the amount divided by one plus the rate and the tax is the amount minus the net. The rate is the percentage divided by 100.
Worked example
With $200 at 15 percent in add mode, the tax is $200 times 0.15, which is $30.00. The total is $200 plus $30, which is $230.00, and the net stays at $200.00. In extract mode the same $200 would be split into about $173.91 net and $26.09 tax.
Related calculators
- Price Increase Calculator: raise a price by a percent.
- Profit Margin Calculator: margin from cost and price.
- Gross Profit Calculator: gross profit on a sale.