GST Calculator

Adding GST to an Exclusive Amount

To add GST, multiply the GST-exclusive amount by the rate, then add that tax to the original amount. At Australia's 10% rate, multiply the amount by 0.1 for GST or by 1.1 for the total.

For example, a taxable commission of $4,500 excluding GST has $450 GST and a $4,950 total. Enter $4,500 and choose GST-exclusive to reproduce it. The Australian Taxation Office (ATO) explains the 10% GST rate, which applies nationally. New South Wales, Victoria, Queensland and Western Australia use the same rate.

The rate field starts at 10%. A custom rate changes the arithmetic only. Setting it to zero does not establish whether a sale is GST-free or input-taxed.

Removing GST From an Inclusive Amount

To remove GST, divide the inclusive total by one plus the rate expressed as a decimal. At 10%, divide by 1.1 for the exclusive amount. Divide the inclusive total by 11 for its GST component.

The starting example uses the ATO's $352 inclusive purchase example. It contains $32 GST and $320 before GST. For a custom rate, the GST component equals the inclusive total multiplied by the rate, divided by one plus that rate.

Correct: $110 including GST contains $10 GST, leaving $100 before tax. Incorrect: subtracting 10% of $110 removes $11 and leaves $99. The 10% rate applies to the exclusive amount, so subtracting 10% of the inclusive total removes too much.

This calculator treats the entered amount as one taxable amount and rounds GST to the nearest cent, with half a cent rounded up. It derives the remaining amount from that rounded GST so the displayed figures add up. The GST Act's rounding rules also address invoices with multiple taxable supplies. Line-by-line invoice rounding can produce a different total.

Checking Whether GST Applies

The calculator separates GST from an amount you identify as taxable. It cannot decide the tax treatment of an invoice, commission or financial supply. For an invoice containing mixed tax treatments, enter only the amount subject to GST.

GST-free sales have no GST in their price. Input-taxed sales also have no GST charged, and include many financial supplies such as lending money. The classification depends on the actual supply, including who provides it and the supplier's GST registration.

For brokerage receipts, use the commission statement's stated tax basis. A $4,950 taxable commission marked GST-inclusive contains $450 GST. A $4,950 amount marked GST-exclusive produces $495 GST and a $5,445 total. Those examples assume the commission is taxable. The lender's treatment of its loan does not establish the tax treatment of the broker's separate service.

Keep taxable commission, other fees and adjustments separate when their tax treatment differs. This single-amount result does not calculate your business activity statement (BAS), GST credits or income tax.