GST Calculator — add or remove 10% GST
Exact to the cent, as you type. Single amounts, whole columns, and a BAS mini-worksheet.
// Enter an amount — the rule used appears here
GST rounded to the nearest cent (half up).
| # | Amount | Ex GST | GST | Inc GST |
|---|---|---|---|---|
| Paste amounts to see the breakdown | ||||
A quick GST position check using your BAS field codes. Amounts are GST-inclusive, as they appear on your reports. This is a rough worksheet — not a lodgement.
One rate, two directions, endless re-typing.
Australian GST is 10%: add it by multiplying an ex-GST price by 0.1, remove it by dividing an inc-GST price by 11. Every merchant, tradie and bookkeeper redoes this arithmetic dozens of times a week — and most online calculators quietly get the cents wrong because they compute in floating point. This one works in exact integer cents, shows the rule it applied, handles whole pasted columns at once, and gives you your rough BAS position. Free, no sign-up, runs entirely in your browser.
The maths, shown honestly.
GST on $100 (ex GST)
| Price ex GST | $100.00 |
| GST (× 0.1) | $10.00 |
| Price inc GST | $110.00 |
// 100 × 0.1 = 10 → 100 + 10 = 110
GST in $1,000 (inc GST)
| Price inc GST | $1,000.00 |
| GST (÷ 11) | $90.91 |
| Price ex GST | $909.09 |
// 1000 ÷ 11 = 90.909… → rounds to 90.91
GST in $59.99 (inc GST)
| Price inc GST | $59.99 |
| GST (÷ 11) | $5.45 |
| Price ex GST | $54.54 |
// 59.99 ÷ 11 = 5.4536… → rounds to 5.45
Straight answers.
How do I calculate GST in Australia?
GST is 10%. To add GST, multiply the ex-GST price by 0.1 and add it: $100 becomes $110. To remove GST from an inclusive price, divide the total by 11 — that eleventh is the GST: $110 ÷ 11 = $10, leaving $100 ex GST.
Why divide by 11 to remove GST?
An inclusive price is 110% of the base: 100% base + 10% GST. The GST share is 10⁄110 of the total — exactly one eleventh. That's why the shortcut is ÷ 11, not "minus 10%" (subtracting 10% from $110 gives $99, which is wrong).
What's GST-free, and how is that different from input-taxed?
GST-free supplies (most basic food, many health and education services, exports) carry no GST, and sellers can still claim GST credits on their inputs. Input-taxed supplies (residential rent, most financial supplies) also carry no GST, but sellers can't claim input credits. Check the ATO's current category lists for your goods — this calculator assumes a standard taxable supply.
How does rounding work?
GST is rounded to the nearest cent, half a cent rounding up. On multi-line invoices the ATO accepts rounding per line or on the invoice total, as long as you're consistent. This calculator rounds half up and shows a note whenever the raw figure needed rounding — so you always know when a cent moved.
Do I need to show GST on invoices?
If you're GST-registered, tax invoices for taxable sales must show the GST — either as its own line or as "total price includes GST". For sales of $82.50 or more (inc GST) your customer needs a valid tax invoice to claim credits. Our free tax invoice generator produces the compliant format automatically.