To add GST in Australia, multiply the price by 1.1; to remove GST from a GST-inclusive total, divide by 11. GST is a flat 10% tax on most goods and services, so a $100 product becomes $110 with GST, and a $110 inclusive price contains exactly $10 of GST. This guide walks through both calculations step by step, with worked examples, the items that are GST-free, and the calculation mistakes that most often trip up Australian small businesses.
Want the answer without the maths? Use the free GST calculator to add or remove 10% GST instantly. Enter any amount and it shows the ex-GST price, the GST component, and the GST-inclusive total side by side.
| Task | Formula | Example |
|---|
| Add GST to an ex-GST price | Price x 1.1 | $500 x 1.1 = $550 |
| Find the GST amount (from ex-GST) | Price x 0.1 | $500 x 0.1 = $50 |
| Remove GST from an inclusive price | Inclusive / 1.1 | $550 / 1.1 = $500 |
| Find the GST amount (from inclusive) | Inclusive / 11 | $550 / 11 = $50 |
The "divide by 11" shortcut is the fastest way to extract the GST component from any GST-inclusive price. It is also the step people most often get wrong, so we cover it in detail in the common mistakes section below.
The Goods and Services Tax (GST) is a broad-based 10% tax on most goods, services, and other items sold or consumed in Australia. It was introduced on 1 July 2000 and is administered by the Australian Taxation Office (ATO).
Australia has a single flat 10% GST rate. Unlike countries with multiple VAT tiers, our system is simple: a sale is either taxable at 10%, GST-free, or input-taxed. There is no reduced rate, which keeps the calculations straightforward once you know the two formulas above.
You must register for GST once your business turnover reaches $75,000 in any rolling 12-month period (looking both back and forward). The threshold is $150,000 for not-for-profits, and $0 (register from day one) if you drive taxi or rideshare. Once registered, you charge GST on your taxable sales and can claim GST credits on your business purchases.
Below $75,000 you can register voluntarily, but you don't have to. If you stay unregistered, you simply don't charge GST and don't claim GST credits, and none of the calculations below apply to your own sales (they still matter for reading supplier invoices).
When you have a price excluding GST and need the GST-inclusive amount:
- Multiply the ex-GST price by 0.1 to get the GST amount.
- Multiply the ex-GST price by 1.1 to get the GST-inclusive total (or just add the GST amount back on).
| Ex-GST Price | GST Amount | GST-Inclusive Price |
|---|
| $100.00 | $10.00 | $110.00 |
| $250.00 | $25.00 | $275.00 |
| $1,500.00 | $150.00 | $1,650.00 |
| $4,200.00 | $420.00 | $4,620.00 |
Worked example. You're a plumber quoting $850 for a hot water system installation (ex-GST):
- GST: $850 x 0.1 = $85.00
- Total invoice: $850 + $85 = $935.00
Your invoice should show both the ex-GST amount and the GST component. (Quoting tradie jobs all day? See how OneBookPlus works for plumbers and other trades businesses.)
When you have a GST-inclusive price and need the ex-GST amount:
- Divide the GST-inclusive price by 11 to get the GST amount.
- Divide the GST-inclusive price by 1.1 to get the ex-GST price.
| GST-Inclusive Price | GST Amount | Ex-GST Price |
|---|
| $110.00 | $10.00 | $100.00 |
| $55.00 | $5.00 | $50.00 |
| $330.00 | $30.00 | $300.00 |
| $2,750.00 | $250.00 | $2,500.00 |
Worked example. You bought office supplies for $88.00 including GST:
- GST component: $88.00 / 11 = $8.00
- Ex-GST price: $88.00 - $8.00 = $80.00
You can claim the $8.00 as a GST credit on your next BAS. When it's time to total those credits up, the free BAS calculator helps you estimate what you owe or are owed.
Not everything attracts GST, so before you apply either formula, confirm the sale is actually taxable. The main GST-free categories are:
- Most basic foods (fresh fruit, vegetables, meat, bread, milk, eggs)
- Not GST-free: prepared meals, restaurant food, snack foods, confectionery, soft drinks
- Most medical and health services
- Prescription medicines
- Private health insurance
- Course fees for accredited courses and related educational materials
- Goods and services exported from Australia
- Sales of existing residential premises (new builds are taxable)
- Precious metals (gold, silver, platinum)
- Water and sewerage services supplied by government
Some things are input-taxed rather than GST-free, which is technically different: no GST is charged on the sale, but you also cannot claim GST credits on related purchases. The main examples are financial services (bank fees, share trading), insurance premiums, and residential rent. By contrast, GST-free suppliers can still claim credits on their inputs.
You're a landscaper and your quote includes:
- Labour: $1,200 (GST applies)
- Plants from a nursery, on-sold: $400 (GST applies)
- A council permit fee you paid on behalf of the client: $150 (may be GST-free if it's a genuine reimbursement/disbursement)
GST on taxable items: ($1,200 + $400) x 0.1 = $160.00
Total invoice: $1,200 + $400 + $150 + $160 = $1,910.00
(Running a landscaping or garden-care business? See OneBookPlus for landscapers.)
If your turnover is under $75,000 and you're not registered, you:
- Do not charge GST on your sales
- Cannot claim GST credits on your purchases
- Do not lodge a BAS (see how to lodge your BAS)
Your invoices should not show a GST amount, and you shouldn't call them "tax invoices": just "invoice" is correct.
You bought a new work ute for $55,000 (inc. GST):
- GST paid: $55,000 / 11 = $5,000
- You claim the $5,000 as a GST credit on your BAS
- Net GST-exclusive cost to your business: $50,000
This only works for business use. If the ute is 70% business and 30% personal, you can only claim 70% of the GST credit ($3,500). Note that the GST credit and the income-tax deduction (including the instant asset write-off) are separate things: the credit reduces your GST liability, the deduction reduces your taxable profit.
The single most common error. $110 minus 10% is $99, which is wrong. Because a GST-inclusive price is 110% of the base amount, the GST inside it is one eleventh of the total, not 10%. Divide by 11 instead: $110 / 11 = $10 of GST, leaving $100 ex-GST.
If you're under the $75,000 threshold and unregistered, adding "GST" to your invoices is not allowed: you'd be collecting a tax you can't remit. Leave GST off entirely and don't label the document a tax invoice.
They look the same on the price tag (no GST charged) but behave differently behind the scenes. GST-free suppliers can still claim GST credits on their inputs; input-taxed suppliers (residential rent, most financial services) cannot. Mixing these up leads to over-claimed credits on your BAS.
If a purchase is partly private (a vehicle, phone, or laptop used personally as well as for work), you can only claim the business-use percentage of the GST credit. Keep a record of how you worked the percentage out.
GST can be rounded to the nearest cent on each line or once on the invoice total, but switching between methods produces totals that don't reconcile. Pick one approach and stick to it; invoicing software applies one method consistently for you.
Only basic food is GST-free. Prepared meals, restaurant and takeaway food, snacks, confectionery, and soft drinks all attract GST. Cafes and food retailers routinely sell a mix of both on one docket.
For taxable sales of $82.50 or more (inc. GST), you must issue a valid tax invoice if the buyer asks for one. It must show:
- The words "Tax Invoice"
- Your ABN
- Date of issue
- A description of the items
- The GST amount for each line (or a statement that the total includes GST)
- The total price including GST
For sales at or below $82.50 you don't need to issue a tax invoice, and a buyer needs one to claim a GST credit only on purchases above that amount.
The ATO requires you to keep all invoices, receipts, and GST records for at least five years. Digital records are fine, just make sure they're backed up.
Don't wait until BAS time to check your numbers. Reconcile your accounts weekly or fortnightly so errors are caught early.
Calculating GST on every invoice and expense by hand is tedious and error-prone. Good invoicing software does it for you and keeps a running GST total ready for your BAS.
OneBookPlus is an all-in-one Australian platform (bookings, invoicing, quotes, jobs, CRM and accounting in one place) built GST/ABN/BAS-native and hosted in AWS Sydney. It calculates GST automatically on every invoice and expense, so you choose whether a line is GST-inclusive, GST-exclusive, or GST-free and the platform does the maths.
What that looks like day to day:
- Automatic 10% GST on all invoices and quotes
- GST-free line items for exempt goods and services
- GST summary reports that line up with your BAS
- Your ABN auto-displayed on every tax invoice
- Expense capture with GST tracking so credits aren't missed
You can do all of this on the $0 free plan with flat, predictable pricing as you grow. See the finance and accounting features or generate a compliant invoice with the free invoice generator.
To add 10% GST, multiply the GST-exclusive price by 1.1 (so $200 becomes $220). To find just the GST portion of an exclusive price, multiply by 0.1. To remove GST from a GST-inclusive total, divide by 11 (so $220 contains $20 of GST).
Because a GST-inclusive price is 110% of the original amount, the GST inside it is 10 parts out of 110, which simplifies to one eleventh. Taking 10% of the inclusive total overstates the GST: $110 x 10% gives $11, but the correct GST component is $110 / 11 = $10.
No. GST registration is only mandatory once your turnover reaches $75,000 in any rolling 12-month period ($150,000 for not-for-profits, or $0 for taxi/rideshare). Under the threshold you can register voluntarily, but if you don't, you don't charge GST and can't claim GST credits.
No. Australia has a single flat 10% GST rate with no reduced tiers. A sale is either taxable at 10%, GST-free (like most basic food and exports), or input-taxed (like residential rent and most financial services).
Stop doing GST maths on the back of a napkin. Try the free GST calculator or the BAS calculator now, or start free with OneBookPlus for automatic GST, professional tax invoices, and BAS-ready reports on the free plan.
