Adding and removing GST the correct way
GST (Goods and Services Tax) is a consumption tax added to most goods and services at the point of sale. In Australia the rate is 10%; New Zealand uses 15%, and the UK's equivalent, VAT, is 20%. This calculator lets you either add GST to a price or work backwards from a GST-inclusive total to find the original amount and the tax component.
How to use the GST calculator
Enter the amount, set the tax rate, and choose whether you want to add tax or remove it. "Add" is useful when you are quoting a customer a GST-inclusive price; "remove" is what you need when a receipt shows a total and you must report the tax you paid.
The maths — and the common mistake
To add GST, multiply by (1 + rate): $100 × 1.10 = $110. To remove GST, you must divide by (1 + rate): $110 ÷ 1.10 = $100. A very common error is to subtract 10% from the inclusive price instead — that gives $99, which is wrong. Subtracting the rate and dividing by (1 + rate) are not the same operation, because the 10% was calculated on the smaller pre-tax figure, not the larger total.
Who needs this
Small-business owners use it to price products and complete Business Activity Statements; freelancers use it to separate the tax from their invoices; and shoppers use it to understand exactly how much tax sits inside a price. Because you can set any rate, the same tool works for VAT, sales tax, or any percentage-based consumption tax worldwide.