The rule
GST included = GST-inclusive price ÷ 11
Price before GST = GST-inclusive price ÷ 1.1 (or price − GST)
Example: $1,100 ÷ 11 = $100 GST, so the price before GST was $1,000.
Why not just take off 10%?
GST was added as 10% of the smaller, pre-GST price. Taking 10% of the bigger, final price over-counts it: 10% of $1,100 is $110, but only $100 of GST was added. Dividing by 11 always undoes it exactly.
Ready reckoner
| Price incl. GST | GST inside (÷ 11) | Price ex GST |
|---|---|---|
| $11 | $1.00 | $10.00 |
| $55 | $5.00 | $50.00 |
| $110 | $10.00 | $100.00 |
| $220 | $20.00 | $200.00 |
| $550 | $50.00 | $500.00 |
| $1,100 | $100.00 | $1,000.00 |
| $2,750 | $250.00 | $2,500.00 |
| $11,000 | $1,000.00 | $10,000.00 |
When you’ll use it
- Checking a tax invoice before claiming a GST credit on your BAS.
- Working out your real income from a fixed “all-inclusive” price, e.g. a $165 service fee includes $15 GST.
- Rideshare and taxi drivers, who must account for 1/11 of every fare as GST.
A note on rounding
The ATO allows GST to be rounded to the nearest cent on the total invoice (0.5 cents rounds up). Small differences of a cent between a receipt and the calculator are normal.
Mixed receipts (for example a supermarket docket with GST-free basic food and taxable items) can’t simply be divided by 11 — only the taxable items carry GST, and the docket usually marks them.
On a spreadsheet
If the GST-inclusive amount is in cell A2, the GST is =A2/11 and the price before GST is =A2/1.1 (or =A2−A2/11). Round with =ROUND(A2/11,2) to keep to cents. For a column of receipts, sum the inclusive amounts first and divide the total by 11 — the answer differs by at most a few cents from rounding each line.
When you prepare your BAS, use the GST amounts actually printed on tax invoices rather than recalculating, because some invoices mix taxable and GST-free items. Accounting apps such as Xero, MYOB and QuickBooks do this division automatically when you mark a transaction as “GST on income” or “GST on expenses”.
And a mental shortcut for round numbers: move the decimal point one place to the left and take away about 9%. For $440, one-tenth is $44, minus about $4 gives $40 — the exact answer, $440 ÷ 11.
Key GST figures (checked 5 November 2026)
| Item | Figure |
|---|---|
| GST rate | 10% |
| GST inside an inclusive price | ÷ 11 |
| Registration threshold | $75,000 GST turnover ($150,000 non-profits) |
| Tax invoice needed for credits | Purchases over $82.50 incl. GST |
| Quarterly BAS due | 28 Oct, 28 Feb, 28 Apr, 28 Jul |
FAQ
How do I calculate GST from a total?
Divide the GST-inclusive total by 11. $1,100 ÷ 11 = $100 GST.
How do I get the price before GST?
Divide the GST-inclusive price by 1.1. $1,100 ÷ 1.1 = $1,000.
How much GST is in $550?
$50. The price before GST is $500.
Sources (checked 5 November 2026): A New Tax System (Goods and Services Tax) Act 1999 (s 9-70 rate of 10%, s 23-15 registration turnover thresholds); ATO “Registering for GST”, “GST-free sales”, “Tax invoices” and “Business activity statements (BAS)” guidance.