- GST is 10% of the base price, not 10% of the GST-inclusive total. This single misunderstanding is behind the majority of GST calculation errors Australian businesses make.
- There are only four formulas you need: × 1.1 (add GST), × 0.1 (find GST amount to add), ÷ 1.1 (remove GST), ÷ 11 (find GST amount inside a price). Everything else is an application of these four.
- GST-free and input taxed are not the same thing. GST-free supplies still allow you to claim input tax credits on related purchases. Input taxed supplies do not. Confusing the two is one of the costliest classification errors a business can make.
GST is 10%. Every Australian business owner knows that. But knowing the rate and calculating it correctly are two very different things.
The moment you need to add GST to a client quote, extract it from a supplier receipt, or reconcile figures for your BAS, the questions start.
- Why can’t you just subtract 10% to remove GST?
- What exactly is the 1/11 rule?
- How do you handle an invoice with both taxable and GST-free items?
In this guide, we break down exactly how to calculate GST in Australia; how to add it, remove it, apply the 1/11 rule correctly, calculate your net GST payable, and handle international transactions.
Always confirm whether your starting price is GST-exclusive or GST-inclusive before applying any formula. Applying × 1.1 to a price that already includes GST means you've charged GST twice and you'll owe the ATO money you never actually collected.
What is the GST calculation formula in Australia?
Before we go into detail, here are the key GST calculation formulas in one place.
|
What you need to do |
Formula |
Example |
|
Add GST to a price |
Price × 1.1 |
$500 × 1.1 = $550 |
|
Find the GST amount you’re adding |
Price × 0.1 |
$500 × 0.1 = $50 |
|
Remove GST from a GST-inclusive price |
Price ÷ 1.1 |
$550 ÷ 1.1 = $500 |
|
Find the GST amount inside a GST-inclusive price |
Price ÷ 11 |
$550 ÷ 11 = $50 |
|
Check if GST is included (quick test) |
Price ÷ 11 = round number? |
$110 ÷ 11 = $10 |
Important distinction
Dividing by 1.1 and dividing by 11 are not the same calculation, they give you different results:
- ÷ 1.1: GST-exclusive price
- ÷ 11: GST amount within the price
Both are correct and both are ATO-accepted methods, we’ll explain exactly how and when to use each one in the sections below.
How do you add GST to a price in Australia?
To add GST in Australia, multiply your GST-exclusive price by 1.1 to get the total price including GST.
What is the formula to add GST?
GST-inclusive price = Base price × 1.1
That’s it. Multiply whatever you’re charging by 1.1 and you have the GST-inclusive price. The reason it’s 1.1 and not just “add 10%” is simple, you’re multiplying by 100% of the price plus the 10% GST on top, which equals 110%, or 1.1 as a decimal.
Example:
Base price (ex-GST) | X 1.1 | GST-inclusive price | GST amount |
$75.00 | X 1.1 | $82.50 | $7.50 |
$350.00 | X 1.1 | $385.00 | $35.00 |
$1,200.00 | X 1.1 | $1,320.00 | $120.00 |
$4,500.00 | X 1.1 | $4,950.00 | $450.00 |
How should GST be shown on invoices?
When quoting a client or issuing a tax invoice, best practice and ATO requirement, is to show three things separately:
- The GST-exclusive price
- The GST amount
- The GST-inclusive total
For example, a $350 service would appear on your invoice as:
Service fee: $350.00 GST (10%): $35.00 Total: $385.00
Important thresholds to know
- For any sale of $82.50 or more (GST-inclusive), you are required to provide a valid tax invoice if your customer requests one.
- For sales over $1,000 (GST-inclusive), the tax invoice must also include the buyer’s Australian Business Number (ABN) or identity.
- Getting this right matters, your customer cannot claim GST credits on their BAS without a valid tax invoice from you.
What is the most common GST calculation mistake when adding GST?
- The error most business owners make is quoting a price and then adding GST on top as an afterthought, only to realise the original price already included GST in their head but not on paper.
- Before you apply the formula, be clear on one thing: is your starting price GST-exclusive (base price) or GST-inclusive (already has GST in it)?
- If it’s already GST-inclusive, you don’t multiply by 1.1, you’re already done.
How do you remove GST from a price in Australia? (and why you can’t subtract 10%)
This is where most GST mistakes happen.
If GST is 10%, it seems logical to subtract 10% to remove it. But that gives the wrong answer.
Why can’t you subtract 10% to remove GST?
GST is calculated on the base price, not the final GST-inclusive amount.
So once GST has been added, the GST portion is less than 10% of the total price.
Here’s the difference:
- GST-inclusive price: $550
- Wrong: $550 − 10% = $495
- Correct: $550 ÷ 1.1 = $500
That $5 difference doesn’t sound like much, but across hundreds of transactions on a BAS, it compounds quickly.
What is the correct formula to remove GST?
GST-exclusive price = GST-inclusive price ÷ 1.1
Example:
GST-inclusive price | ÷ 1.1 | GST-exclusive price | GST amount |
$82.50 | ÷ 1.1 | $75.00 | $7.50 |
$385.00 | ÷ 1.1 | $350.00 | $35.00 |
$1,320.00 | ÷ 1.1 | $1,200.00 | $120.00 |
$4,950.00 | ÷ 1.1 | $4,500.00 | $450.00 |
When do you need to remove GST from a price?
The most common scenarios where you need to extract the GST-exclusive price from a GST-inclusive amount:
- Supplier receipts and invoices: When a supplier charges you $385 including GST, the GST credit you can claim on your BAS is $35, not $38.50 (which is what you’d get by incorrectly taking 10% of $385)
- Pricing reviews: If you’ve been quoting GST-inclusive prices and need to report the GST-exclusive revenue figure on your tax return
- Reconciling accounts: Ensuring your accounting software is coding transactions to the correct GST-exclusive amount
Note: You can only claim GST credits on purchases that are for business purposes and where you hold a valid tax invoice. Personal expenses, input taxed purchases (such as residential rent), and GST-free purchases do not entitle you to a GST credit, regardless of the calculation.
Businesses making predominantly GST-free supplies like exporters, certain healthcare providers, often end up in a net GST refund position every quarter. This is not a red flag. It's the correct outcome of the system working as intended. Clean records and consistent lodgement make refunds straightforward.
What is the 1/11 rule for GST in Australia?
If you’ve ever seen an accountant calculate GST from a receipt almost instantly, this is likely what they’re using.
The 1/11 rule is the fastest way to extract the GST amount from any GST-inclusive price and once you understand it, it becomes second nature.
Why does the 1/11 GST rule work?
GST amount = GST-inclusive price ÷ 11
That’s it. Divide any GST-inclusive price by 11, and you get the GST component, no extra steps needed.
Why it works
When GST is added to a price, the total becomes 11 parts:
- 10 parts = base price
- 1 part = GST
So GST is always 1/11 of the total price.
Mathematically:
GST-inclusive price = Base price + 10% of base price = Base price × 1.1
Therefore: Base price = GST-inclusive price ÷ 1.1
And: GST amount = GST-inclusive price − Base price = GST-inclusive price ÷ 11
Example:
GST-inclusive price | ÷ 11 | GST amount | GST-exclusive price |
$110.00 | ÷ 11 | $10.00 | $100.00 |
$385.00 | ÷ 11 | $35.00 | $350.00 |
$1,650.00 | ÷ 11 | $150.00 | $1,500.00 |
$5,500.00 | ÷ 11 | $500.00 | $5,000.00 |
Should you use the 1/11 rule or divide by 1.1?
Both are correct and both are ATO-accepted. The difference is simply what you’re trying to find:
You need to find | Use this |
The GST amount inside a price | ÷ 11 (1/11 rule) |
GST-exclusive price | ÷ 1.1 |
In practice, the 1/11 rule is most useful when you’re working through receipts and invoices and need to quickly identify the GST component for BAS preparation or input tax credit claims, without first calculating the base price.
What is the difference between GST-free, input taxed and taxable supplies?
The difference is how GST is applied: taxable supplies include 10% GST, GST-free supplies have no GST but allow credits, and input taxed supplies have no GST and no credits.
1. Taxable supplies: 10% GST applies
Most goods and services sold in Australia fall here. You charge 10% GST on the sale and you can claim input tax credits on related business purchases.
Common examples:
- professional services,
- consulting,
- trade services,
- retail goods,
- software,
- advertising,
- commercial rent,
- equipment hire.
2. GST-free supplies: 0% GST, but credits still apply
GST-free supplies are charged at 0%, meaning you do not add GST to the sale price. Importantly, even though you’re not charging GST, you can still claim input tax credits on purchases you make to produce those GST-free supplies.
Common examples under Australian law:
- Most basic food (fresh fruit, vegetables, bread, meat but not restaurant meals or hot takeaway food)
- Most exports of goods and services to recipients outside Australia
- Most health services (GP consultations, hospital treatment, certain allied health)
- Most education courses provided by recognised institutions
- Certain childcare services
- Certain medicines and medical aids
3. Input taxed supplies: No GST, no credits
Input taxed supplies are fundamentally different from GST-free supplies and this is where the most costly mistakes happen. With input taxed supplies, you do not charge GST on the sale but you also cannot claim input tax credits on purchases related to making those supplies.
Common examples:
- Residential rent and residential property sales
- Most financial supplies (lending money, providing credit, life insurance)
- Precious metals (in certain circumstances)
The practical impact: if you’re a landlord charging residential rent, you don’t add GST to rent invoices but you also can’t claim back the GST on repairs, maintenance, or property management fees related to that property. Those GST amounts become a cost, not a credit.
Why do GST categories matter for your business?
If you’re making input taxed supplies, GST on related expenses becomes a real cost.
For example:
A landlord renting residential property:
- Does not charge GST on rent
- Cannot claim GST on repairs, maintenance, or management fees
That GST becomes an expense, not a credit.
How do you calculate your net GST payable?
Understanding the individual formulas is one thing. But what Australian business owners actually need to know is how those formulas come together to give you one final number, the amount you owe the ATO, or the refund you’re entitled to, at the end of each BAS period.
Here’s the complete process from start to finish.
What is the GST payable formula?
Net GST Payable = GST Collected on Sales − GST Credits on Purchases
If the result is positive, you owe that amount to the ATO. If the result is negative, the ATO owes you a refund.
Step 1: Calculate your GST collected (Output tax)
Add up all the GST you charged on taxable sales during the BAS period. Using the formulas we covered earlier:
- If your sales figures are GST-exclusive: Total taxable sales × 0.1 = GST collected
- If your sales figures are GST-inclusive: Total taxable sales ÷ 11 = GST collected
Example:
Total taxable sales for the quarter (GST-exclusive): $45,000 GST collected: $45,000 × 0.1 = $4,500
Only include taxable supplies here. GST-free and input taxed sales do not contribute to GST collected.
Step 2: Calculate your GST credits (Input tax credits)
Add up all the GST you paid on eligible business purchases during the same period. Again using the 1/11 rule if your expense figures are GST-inclusive:
- Total eligible business purchases (GST-inclusive) ÷ 11 = GST credits claimable
Example:
Total eligible business purchases for the quarter (GST-inclusive): $16,500 GST credits: $16,500 ÷ 11 = $1,500
Only include purchases that are:
- For business purposes (not private)
- From GST-registered suppliers
- Supported by a valid tax invoice for amounts of $82.50 or more (GST-inclusive)
- Not related to input taxed supplies
Step 3: Calculate your net GST position
- GST collected: $4,500
- GST credits: $1,500
- Net GST payable: $4,500 − $1,500 = $3,000
This $3,000 is what gets reported and paid to the ATO when you lodge your BAS.
What happens if your GST credits are higher than GST collected?
This happens, particularly for businesses in early growth stages with high setup costs, or businesses that make predominantly GST-free supplies (like exporters). In this case your net position is negative and the ATO will refund the difference.
- GST collected: $800
- GST credits: $1,400
- Net GST refund: $600
The ATO typically processes GST refunds within 14 days of a lodged BAS, provided your BAS is accurate and your records are in order.
Step 4: Report on your BAS
Once you have your net GST figure, it gets reported on your BAS under the relevant labels:
- G1 (total sales),
- G2 (export sales),
- G3 (other GST-free sales),
- G10 (capital purchases),
- G11 (non-capital purchases), and
- 1A (GST on sales) and 1B (GST credits).
Your net GST payable or refund flows from the difference between 1A and 1B.
This is where accurate bookkeeping throughout the quarter pays off, if your records are clean, your BAS figures are simply a matter of pulling the right reports. If they’re not, this is the step where errors surface.
Read our complete guide on How to Lodge BAS in Australia
Voluntary GST registration below the $75,000 threshold can actually work in your favour. If your business makes significant purchases, you can claim back the GST on those expenses even before you're required to register, improving cash flow from day one.
How does GST work for international transactions and foreign currency?
If your business deals with overseas customers or suppliers, GST doesn’t disappear, it just becomes more nuanced.
1. Do you charge GST on overseas customers?
Most exports are GST-free (0%), meaning you don’t charge GST, but only if certain conditions are met.
- Goods: Must leave Australia within 60 days of invoice or payment
- Services: Usually GST-free if the customer is overseas and the service isn’t connected to goods or property in Australia
Key point: It’s not just where the customer is, it’s how and where the service is used.
2. Do you pay GST on imported goods and services?
Imported goods:
GST applies to most imports, but how it’s collected depends on value:
- Over $1,000 → collected at the border
- Under $1,000 → collected by the supplier/platform
If you’re GST-registered, this is generally claimable as an input tax credit.
Imported digital services:
GST may apply to subscriptions, software, and online services.
- If GST is charged → you may be able to claim it
- If not → reverse charge rules may apply
How do you calculate GST on foreign currency transactions?
When a transaction is denominated in a foreign currency, you must convert the amount to Australian dollars to calculate GST correctly.
- The ATO requires you to use the exchange rate applicable on the date of the transaction, either the rate published by the Reserve Bank of Australia (RBA) or a rate from a recognised financial institution.
Example: You invoice a US client for USD $5,000 for consulting services. AUD/USD exchange rate on invoice date: 0.65 AUD equivalent: USD $5,000 ÷ 0.65 = AUD $7,692.31
- If the supply is taxable (i.e. not GST-free), GST would be calculated on the AUD equivalent.
- If it’s an export and meets the GST-free conditions, no GST applies, but you still need to record the AUD value accurately for BAS reporting.
How can Sleek help you manage GST and BAS accurately?
GST mistakes don’t stay isolated, they flow through to your BAS, your tax return, and your ATO compliance record. Fixing them later is far more expensive than getting them right from the start.
With Sleek, you get:
- Correct GST setup from day one: We ensure your business is registered correctly, your supplies are classified properly (taxable, GST-free, input taxed), and your reporting cycle is aligned with your obligations
- Accurate BAS preparation and lodgement: Registered BAS agents handle your GST calculations every period, so what you collect, claim, and report is consistent and ATO-compliant
- Clean, GST-ready books: Every transaction is coded correctly, so your GST figures are always accurate and your BAS is ready when you need it
- No missed deadlines or penalties: We manage your lodgement schedule and ensure everything is submitted on time, so you avoid interest charges and ATO follow-ups
- Transparent, fixed pricing: Clear, upfront pricing so you only pay for what you need and avoid unexpected costs.
Stop second-guessing your GST calculations. Talk to a Sleek accountant and get it handled correctly from here. Schedule a call now.
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Frequently Asked Questions
How does GST work on imported goods in Australia?
For goods imported with a customs value over $1,000 AUD, GST is calculated on the customs value plus duty, freight, and insurance costs.
For goods under $1,000 AUD, overseas suppliers registered for GST in Australia collect GST at the point of sale. If your business is GST-registered and the goods are for business use, you can claim the GST back as an input tax credit on your BAS.
What is the 1/11 rule for GST in Australia?
The 1/11 rule is a quick way to calculate the GST amount from a GST-inclusive price. Since the total price includes 10% GST (making it 110% of the base price), the GST component is always 1/11 of the total. For example, $385 ÷ 11 = $35 GST.
Should I use a GST calculator or calculate GST manually?
For a single invoice or quick calculation, either works, the formulas are straightforward once you know them.
But across a full quarter of transactions, mixed supply types, foreign currency, and BAS reconciliation, manual calculations and basic calculators leave too much room for error. That’s where a registered accountant ensures every figure is coded correctly, every credit is claimed, and your BAS reflects your actual GST position, not an approximation of it.
