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GST Calculator
On a small screen, scroll the table sideways to see every column.
| What you have | Choose | Example at 10% |
|---|---|---|
| A price excluding GST | Add GST to the amount | A $1,000 exclusive price becomes $1,100 including $100 GST. |
| A total including GST | Remove GST from the amount | $1,100 inclusive contains $100 GST and a $1,000 exclusive price. |
| An exclusive price and only need its tax | GST on an amount excluding GST | GST on a $1,000 exclusive price is $100. |
| An amount with no GST to calculate | 0% | The calculator leaves the amount unchanged; it does not classify the sale. |
Why removing GST is not subtracting 10%
The standard GST amount is 10% of the exclusive price. Once added, it represents one-eleventh of the inclusive total. Subtracting 10% from $1,100 would remove $110, which is $10 too much.
The calculator divides an inclusive total by 1.1 to find the exclusive amount, then subtracts that amount from the total to find GST. Results are displayed to two decimal places.
Choose the right amount
Use the part of the transaction to which the selected GST treatment applies. A mixed invoice containing taxable and GST-free items cannot necessarily be treated as one fully taxable total. Check the supplier's tax invoice and the underlying transaction.
The “GST amount” option starts from an amount excluding GST. If the figure already includes GST, use the removal option instead.
Split a mixed invoice before calculating
Suppose an invoice contains $1,100 of fully taxable items, including GST, and $200 of items with no GST included. The taxable component contains $100 GST, and the total cash payment is $1,300. Dividing the entire $1,300 by 11 would produce $118.18 and overstate the GST in this assumed example.
Use the supplier's treatment to identify the relevant component; the calculator cannot classify the items for you. Enter $1,100 using the removal option for the taxable component and keep the $200 separate. Add the components again when checking the total invoice payment.
Keep inclusive and exclusive figures consistent
For a price quoted as $850 plus GST, enter $850 using the add option to get $935 including $85 GST. If the quoted total is already $935 inclusive, use the removal option to recover the same figures. Selecting add on an inclusive amount would calculate GST a second time.
When comparing suppliers, put both quotes on the same basis. A $1,000 exclusive quote and a $1,050 inclusive quote cannot be compared fairly as though both were the final payment. First establish the tax treatment and full cash price, then consider any eligible credit separately.
Results are rounded for display. Small differences can arise when an invoice rounds individual lines and you calculate from an aggregated amount. Reconcile to the actual tax invoice and accounting records; do not change a recorded tax amount solely to match a simplified calculator total.
What this calculator does not decide
It does not determine whether you must register for GST, whether a sale is taxable, GST-free or input taxed, whether a GST credit is available, or when an amount belongs on a BAS. Selecting 0% simply performs a zero-tax calculation.
Your net BAS position depends on more than the GST component of one sale. The ATO explains how GST works (checked 5 October 2026). Use the applicable guidance and your business records for reporting, and obtain advice where the treatment is unclear.
Keep the invoice payment separate from a possible GST credit
On a fully taxable $1,100 supplier invoice, the calculated GST component is $100. The supplier may still need the full $1,100 paid by the due date. Any entitlement to a credit and the timing of reporting or recovery are separate questions.
Use the inclusive figure for the cash leaving the bank account and record the GST component separately. That avoids understating the cash needed merely because the business expects to claim a credit.
If the issue is funding an existing ATO debt, use the separate tax debt guide to compare borrowing with an available payment arrangement. The arithmetic here helps identify an invoice component; the debt decision needs the full tax account and a repayment forecast.
Sources and further reading
Disclaimer: smbloan.com.au does not directly provide GST lending or accounting services. This content and calculator are for informational purposes only. Consult qualified professionals for specific GST and lending advice.