Key takeaways
- To add GST: multiply the GST-exclusive price by 1.1.
- To find the GST in a GST-inclusive price: divide by 11.
- To remove GST: divide the GST-inclusive price by 1.1.
- Don't take 10% off a GST-inclusive price — that overstates the GST.
GST in Australia is 10%. The calculations are simple once you know which price you're starting from.
The three formulas
| You want to… | Formula | Example |
|---|---|---|
| Add GST to a price | Price × 1.1 | $500 × 1.1 = $550 |
| Find the GST in a GST-inclusive price | Price ÷ 11 | $550 ÷ 11 = $50 |
| Remove GST from a price | Price ÷ 1.1 | $550 ÷ 1.1 = $500 |
The most common mistake
Taking 10% off a GST-inclusive price gives the wrong answer. On a $550 price, 10% is $55 — but the GST included is only $50. Always divide a GST-inclusive amount by 11 to find the GST.
Mixed invoices
Some invoices include both taxable and GST-free items — a supermarket receipt, for example. Only the taxable items include GST. Check the tax invoice, which should show the GST amount or state that the total includes GST.
Rounding
Rounding GST to the nearest cent is acceptable. When adding up many transactions, small rounding differences are normal; your accounting software will handle them consistently.
Official sources
General information only. This article doesn't take into account your personal circumstances and isn't a substitute for professional advice. Tax rules and thresholds change — check current details with the ATO or contact us for advice specific to you.
Published by
ANS Taxation & Accounting
Melbourne accounting and tax practice