GST calculator

Australia’s GST rate is a flat 10%. This calculator either adds GST onto a price that doesn’t have it yet, or works out how much GST is hiding inside a price that already includes it.

It can help you answer questions like:

• What should I actually charge a customer, GST included?
• How much GST have I collected on a sale?
• What’s the real pre-tax amount on this receipt or invoice?

What you’ll need to enter:

• Amount — the dollar figure you’re starting with. (Example: $100.)
• I want to — choose “Add GST” if your amount doesn’t include GST yet (like a quoted cost price), or “Remove GST” if it already includes GST (like a receipt or invoice total) and you want to see the GST portion and the amount before tax.

How it works
Adding GST means multiplying your amount by 10% and adding that on. Removing GST means working out what 10% of the final price actually was, which isn’t quite the same as just taking 10% off — we handle that calculation for you either way.

What the result tells you
With the example amount of $100 and “Add GST” selected, the GST component is $10 and the total to charge is $110.

A few things worth knowing when working with GST:

1. Always check which way you’re going. Mixing up “add” and “remove” is one of the most common invoicing mistakes — this calculator labels both clearly so you can double-check before sending an invoice.
2. Quoted prices should say whether GST is included. Being clear with customers upfront (e.g. “$110 including GST”) avoids awkward conversations later.
3. Keep this handy at tax time. Quickly checking GST on individual transactions can help spot errors before they end up on your BAS.
4. When in doubt, ask your bookkeeper. This calculator handles the maths, but GST rules can get more complex for certain transactions, exports, or GST-free items.

In short: a quick, reliable way to check GST on the fly, without reaching for a spreadsheet.