Australia GST Calculator

How to use this calculator

1. Enter amount — The calculator loads with a worked example already filled in, so you can see what a realistic set of figures looks like before replacing them with your own.
2. Fill in the remaining fields — Every field has a sensible default. Change the ones that apply to you and leave the rest.
3. Read the result — The answer updates as you type — there is nothing to submit. The rows beneath the headline show how it breaks down.
4. Expand the schedule — Where a year-by-year table is offered, open it. The breakdown over time usually shows something the single headline figure does not.
5. Share or print — Use the share button to copy a link with your figures already filled in, or print the result — the print stylesheet strips the navigation and adverts.

What this calculator works out

To use the Australia GST Calculator, enter your amount, GST rate and supply type. The result — total including GST — updates as you type, with no button to press and nothing to submit. The calculation runs entirely in your browser, so the figures you enter are never sent anywhere. The rules applied are those published by the Australian Taxation Office (ATO).

How this is calculated

Adding tax multiplies the net amount by one plus the rate. Extracting tax from a gross amount divides by one plus the rate — it does not subtract the rate, which is the mistake that produces a figure several percent out. On £120 including 20% VAT the tax is £20, not £24, because the tax is a fifth of the net rather than of the gross.

A worked example

Take the values this page loads with:

• Amount: A$10,000.00
• GST rate: 18%
• Supply type: Within the state (CGST + SGST)
• Amount entered is: Before GST (add GST)

On those figures the total including gst is 11,800.00. Broken down:

• Amount before GST: 10,000.00
• Total GST: 1,800.00
• CGST (9.00%): 900.00
• SGST (9.00%): 900.00
• Total including GST: 11,800.00

Change any field above and every figure here recalculates — these numbers are produced by the same formula the calculator runs, so they cannot drift apart from it.

What the figures mean

The headline figure answers the immediate question. These are the ones worth paying attention to:

• Total GST — the figure worth watching when you change your inputs.
• CGST (9.00%) — the figure worth watching when you change your inputs.
• SGST (9.00%) — the figure worth watching when you change your inputs.

Where a schedule is shown, expand it: the year-by-year breakdown usually reveals something the single headline number hides.

What this calculator assumes

Intra-state supplies split the rate evenly into CGST and SGST. Extracting GST from an inclusive price divides by (1 + rate) — subtracting the rate from the gross gives the wrong answer.

Why it runs in your browser

Every calculation on this page is arithmetic, and arithmetic does not need a server. Running it locally means the result is instant, it keeps working if your connection drops, and — the part that matters — your salary, your debts and your medical measurements are never transmitted to us. There is no figure on our side to store, log or lose.

Where this calculator stops

A calculator applies the rules it is given to the figures you enter. It cannot see the rest of your circumstances, and real financial decisions are rarely decided by a single number.

Treat the result as a starting point for a conversation — with a lender, an accountant or an adviser — rather than as an answer. Where an institution will quote you a real figure, that figure is the one that counts: it will include fees, your credit profile and terms this page knows nothing about.

Keeping the figures current

The formula behind this page does not change, but the assumptions you should bring to it do — interest rates, inflation and market returns all move. Revisit the inputs rather than trusting a figure you calculated a year ago.