GST Calculator

GST is one of those things that sounds simple until you're staring at an invoice wondering whether the price already includes it. If you've ever caught yourself doing shaky mental maths in front of a client, this calculator saves you from that little moment of panic.

A practical example: say you're a freelance designer quoting $1,850 ex GST for a logo package. Add 10% GST and the tax is $185, which makes the total $2,035 inc GST. Going the other way matters too. If a supplier gives you a bill for $330 inc GST, the GST portion is $30 and the GST-exclusive amount is $300. That's the number you actually want if you're checking margins, comparing quotes, or sorting your BAS records.

How to get the most out of this

Start by being clear on whether the number in front of you is GST-inclusive or GST-exclusive. That's where most mistakes happen. If you're quoting customers, use the "Add GST" option so your final total looks clean and professional. If you're reviewing receipts or invoices you've already paid, use "Remove GST" to see the real pre-tax cost. And if you're just trying to work out how much GST sits inside a total, the GST-only mode is the fastest path.

One small but important thing: don't just subtract 10% from a GST-inclusive amount. That gives the wrong answer. To remove GST properly, you divide by 1.1. It sounds minor, but on bigger numbers the gap gets annoying fast.

The divide-by-11 shortcut

If you already have a GST-inclusive price and only want the GST component, divide the total by 11. Example: $330 ÷ 11 = $30 GST. Then the GST-exclusive amount is $330 - $30 = $300. Same answer as dividing $330 by 1.1, just faster for invoice checks.

GST-free vs input-taxed is not the same thing

A lot of people mash these together, but they are different. GST-free supplies can still let the business claim GST credits on related business purchases. Common examples include many basic food items, some health services, and some education. Input-taxed supplies, like residential rent and many financial supplies, generally do not charge GST and also usually do not let you claim GST credits on related inputs.

The $75,000 threshold

If your business turnover is $75,000 or more, you generally need to register for GST in Australia. Below that, many small operators can stay unregistered, which means they usually do not add GST to invoices and cannot claim GST credits in the normal way. That threshold matters a lot for freelancers, tradies, consultants, and side businesses crossing from hobby territory into real business territory.

BAS and invoice use

This calculator is handy when you are checking whether an invoice amount is already GST-inclusive, working backwards from a receipt, or figuring out what portion belongs in your BAS records. It is also useful when quoting clients because you can show the clean ex-GST price and the final total without doing fiddly mental maths.

Official reference: ATO GST guidance. Threshold and GST treatment should always be checked against the ATO if you are doing more than simple quote maths.

FAQs

Why can't I just take 10% off a GST-inclusive price?

Because GST is 10% of the original pre-tax amount, not 10% of the final total. A $110 total contains $10 GST, not $11.

Are all Australian purchases subject to GST?

Not quite. Basic food, many health services, education, and residential rent are common examples people run into, but GST-free and input-taxed are not the same thing. Most ordinary goods and services still include GST.

Should I round GST to the nearest cent?

Usually, yes. For everyday invoices and quotes, rounding to two decimal places keeps things tidy and lines up with how amounts are normally shown in Australia.