To reverse GST in Australia, divide the GST-inclusive total by 11. That gives you the GST included in the price. Subtract it from the total (or multiply the total by 10 and divide by 11) to get the price before GST. This works because GST is 10% of the pre-tax price, which is exactly one-eleventh of the GST-inclusive price.
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How to reverse GST, step by step
The GST-inclusive price is 110% of the price before GST, so the GST portion is 10/110 — one eleventh — of the total:
- GST included = total ÷ 11
- Price before GST = total − GST = total × 10 ÷ 11
Worked example 1 — a $110.00 invoice
$110.00 ÷ 11 = $10.00 GST. Price before GST = $110.00 − $10.00 = $100.00.
Worked example 2 — a $50.00 receipt
$50.00 ÷ 11 = $4.5454…, which rounds to $4.55 GST. Price before GST = $50.00 − $4.55 = $45.45. GST amounts are rounded to the nearest cent.
Worked example 3 — a $27.50 charge
$27.50 ÷ 11 = $2.50 GST, leaving $25.00 before GST.
Why you divide by 11, not take 10%
Ten per cent of a GST-inclusive total overstates the GST. Ten per cent of $110 is $11 — but the GST inside a $110 price is only $10, because the 10% was added to $100, not to $110. Dividing by 11 reverses the calculation correctly. Taking 10% of the total is the most common reverse-GST error.
Common mistakes
- Subtracting 10% of the total. That removes too much. Always divide the inclusive total by 11.
- Assuming every price includes GST. GST-free supplies (most basic food, many health and education services) and input-taxed supplies (residential rent, most financial supplies) carry no GST to extract.
- Reversing GST on a mixed total. If a total combines taxable and GST-free items, dividing the whole amount by 11 overstates the GST — reverse only the taxable portion.
- Rounding too early. Round only the final GST figure to the nearest cent, not the intermediate steps.
Frequently asked questions
How do I remove GST from a total in Australia?
Divide the GST-inclusive total by 11. The result is the GST included in the price; the remainder is the price before GST.
What is the formula for reverse GST?
GST = total ÷ 11, and price before GST = total × 10 ÷ 11. Both follow from GST being 10% of the pre-tax price.
Is GST always 10% in Australia?
The GST rate has been 10% since GST commenced on 1 July 2000. Some supplies are GST-free or input-taxed, so not every price includes GST.
How do I find the price before GST?
Subtract the GST from the total, or multiply the total by 10 and divide by 11. For a $110.00 total that is $100.00.