How Australian GST works
GST is a 10% broad-based tax on most goods and services sold in Australia. GST-registered businesses collect GST from customers, pay GST to suppliers, and remit the net amount to the ATO via the Business Activity Statement (BAS). The arithmetic is the same in every direction; the work is in picking the right treatment.
Standard (10%)
Most goods and services sold by a GST-registered business: office supplies, professional services, software, restaurant meals, retail goods, commercial rent.
GST-free (0%)
Taxable at 0%, but the supplier can still claim input-tax credits on related purchases. Basic food, most health and medical services, most education, water and sewerage, and exports.
Input-taxed (no GST)
No GST charged and no input-tax credit on related purchases. Most financial supplies (bank fees, interest, lending), residential rent, sales of existing residential premises.
Out of scope
Outside the GST system entirely. Government taxes and regulatory charges covered by the GST Determination (ASIC fees, council rates, stamp duty, land tax).
The one-eleventh rule explained
For any GST-inclusive amount at the standard rate, the GST component is exactly the gross divided by 11. The arithmetic: adding 10% to a net of $100 produces $110, and $110 divided by 11 returns $10, the original GST. The calculator surfaces this as a dedicated row so you can cross-check the figure on a supplier invoice without reaching for a separate worksheet.
Common scenarios
Adding GST to your own invoice. Sell at $500 net, GST-registered, standard-rated, your customer pays $550 gross. Pick Add GST, type 500, supply type Standard 10%.
Extracting GST from a supplier receipt. Receipt shows $99 GST-inclusive at the standard rate. GST is $9 (99 divided by 11), net is $90. Pick Extract GST, type 99, supply type Standard 10%.
GST-free purchase. A basic food invoice for $50 carries no GST. The calculator confirms the gross equals the net.
Input-taxed. A bank fee for $4.50 carries no GST and no input-tax credit. Use input-taxed to confirm zero recoverable GST.