Australia GST Calculator 2026: Add, Remove and Reverse GST

GST in Australia at a glance

GST in Australia is a 10% tax on most goods and services, charged by businesses registered for GST and paid to the Australian Taxation Office (ATO). The rate is the same in every state and territory and has not changed since GST began on 1 July 2000.

How much is GST on $100?

GST on $100 is $10, so a $100 price before GST becomes $110 including GST. Going the other way, a $100 price that already includes GST contains $9.09 of GST, because GST is 1/11 of an inclusive price, not 10% of it.

How to calculate GST: formulas

To calculate GST in Australia, multiply a GST-exclusive price by 10% to get the GST, or by 1.1 to get the GST-inclusive price. To find the GST inside a GST-inclusive price, divide it by 11; to remove GST, divide the inclusive price by 1.1.

Why GST is 1/11 of an inclusive price, not 10%

An inclusive price is 110% of the exclusive price, so GST makes up 10 parts in 110, which is 1/11. Taking 10% off $110 gives $11, which is wrong; dividing by 11 gives the correct $10. This is the most common GST mistake.

Rounding GST

GST is rounded to the nearest cent, with half a cent rounded up. On an invoice with several taxable items you can round the GST on each line or once on the total, but use the same method every time.

How to use the GST calculator

1. Choose what to work out. One amount, a full invoice, or the GST figures for your business activity statement (BAS).
2. For one amount, pick add or remove. Add GST if your price is before GST; remove GST if it already includes GST, like a receipt or shelf price.
3. For an invoice, enter each line. Say whether amounts include GST, then untick GST on any GST-free item. Add up to 20 lines.
4. For your BAS, enter the period's totals. Taxable sales including GST, GST-free sales and purchases that include GST.
5. Read the result. The receipt shows GST, the price before and after GST, and any tax invoice rules that apply.
6. Save or copy it. Download a PDF or CSV, or copy the figures to paste into an invoice or spreadsheet.

Worked GST examples

Each example uses the same rules as the calculator, with GST rounded to the nearest cent.

GST quick reference table

Common amounts with GST added, and the GST contained in the same amount when it already includes GST.

When does GST apply in Australia?

GST applies to taxable sales made in Australia by a business registered or required to be registered for GST. Some sales are GST-free and some are input-taxed, so a GST-registered business does not charge GST on everything it sells.

Is GST different in NSW, Victoria or Queensland?

No. GST is a federal tax at 10% in every state and territory, so a GST calculator for New South Wales, Victoria, Queensland or anywhere else gives the same answer. State taxes such as stamp duty are separate and do vary; see the stamp duty calculator Australia.

GST-inclusive vs GST-exclusive prices

A GST-inclusive price already contains the 10% GST; a GST-exclusive price, often written ex GST, does not. Prices shown to consumers must generally include GST under the Australian Consumer Law, while business quotes and wholesale price lists are often ex GST.

When a price is quoted without saying, ask. On a $5,000 job the difference is $500: $5,000 ex GST costs $5,500, while $5,000 including GST costs $5,000 with $454.55 of GST inside it.

How to calculate GST payable on your BAS

GST payable on a business activity statement is the GST you collected on sales (label 1A) minus the GST you paid on business purchases (label 1B). If 1B is larger, the ATO refunds the difference.

1. G1 Total sales. All sales for the period, including GST, including GST-free sales.
2. 1A GST on sales. Your taxable sales including GST, divided by 11.
3. 1B GST on purchases. Business purchases that include GST, divided by 11. You need a tax invoice for purchases over $82.50 including GST.
4. Net GST. 1A minus 1B: pay it if positive, receive a refund if negative.

Quarterly BAS are generally due on 28 October, 28 February, 28 April and 28 July; tax and BAS agents can get later dates. Businesses with turnover under $10 million can use simpler BAS, reporting only G1, 1A and 1B, and can account for GST on a cash basis.

Do you need to register for GST?

You must register for GST within 21 days once your business's GST turnover reaches $75,000 a year, or $150,000 for a non-profit organisation, and taxi and ride-sourcing drivers must register whatever their turnover. Turnover is tested both over the past 12 months and as expected for the next 12.

Below the threshold, registering is optional. Registering lets you claim GST credits on business purchases, but you must then charge GST on taxable sales and lodge BAS. A business that is not registered must not charge GST or show GST on its invoices.

Tax invoices and GST

A GST-registered business must give a tax invoice within 28 days if a customer asks for one on a taxable sale over $82.50 including GST. Invoices of $1,000 or more must also show the buyer's identity or ABN.

A tax invoice shows the words tax invoice, the seller's name and ABN, the date, a description of what was sold, and the GST amount or a statement that the total includes GST. Keep tax invoices for purchases: you need them to claim GST credits over $82.50.

GST on imports and overseas purchases

Goods worth $1,000 or less bought from overseas sellers usually include 10% GST at checkout, because large overseas sellers must register and collect it. Goods over $1,000 have GST, and sometimes customs duty, collected at the border before delivery.

Digital products and services bought from overseas businesses, such as streaming and software subscriptions, also include GST. Use the calculator's remove mode to see the GST in an overseas price shown in Australian dollars.

Common GST calculation mistakes

Most GST errors come from taking 10% off an inclusive price or charging GST where it does not apply.

1. Taking 10% off an inclusive price. GST in $1,100 is $100 (1/11), not $110.
2. Dividing by 10 to remove GST. $1,100 ÷ 1.1 = $1,000; $1,100 − 10% gives the wrong $990.
3. Charging GST on GST-free items. Most basic food, many medical services and exports have no GST.
4. Charging GST when not registered. Only registered businesses can charge GST.
5. Claiming credits without a tax invoice. Purchases over $82.50 including GST need one.
6. Mixing rounding methods. Round GST per line or per invoice, but use one method consistently.

How close is this calculator?

For taxable sales at the standard 10% rate the results are exact to the cent, using the same formulas as the ATO and the government's Moneysmart GST calculator. It does not work out special cases such as the margin scheme on property, GST on second-hand goods bought for resale, or adjustments, for which you should check ATO guidance or a registered BAS agent.