GST Calculator

How to use

Pick a direction, type one number, and read the other two. Remove starts from a GST-inclusive total and splits it into net and tax — that is the receipt and expense-claim case. Add starts from your price before tax and gives you the figure to invoice. Choose the rate that applies to what you're selling or buying; the 10% gst is right far more often than not.

The working is shown as arithmetic rather than just a result, so you can check it or repeat it without the tool.

Removing GST: divide, don't subtract

This is the calculation the tool exists for, and the one hand arithmetic gets wrong. Take a $120.00 total at 10%:

• Correct: $120.00 ÷ 1.10 = $109.09 net, so GST = $120.00 − $109.09 = $10.91.
• Wrong: 10% of $120.00 = $12.00, which overstates the tax by $1.09 and understates the net by the same amount.

The reason is that 10% was never applied to $120.00. It was applied to $109.09, and the total is what came out. To undo a multiplication you divide by the same factor, which is why 1.10 — not 10% — is the number that appears in the sum. The shortcut worth memorising: at 10% the tax is exactly 1/11 of any GST-inclusive total.

Adding GST: the easy direction

Multiply by 1.10. A $250.00 fee becomes $275.00 on the invoice, of which $25.00 is GST you are collecting rather than earning. Nobody miscalculates this one — but plenty of new traders quote $250.00 to a customer, forget they must now add tax to it, and end up absorbing $25.00 out of their own margin because the price was already agreed. If you have just registered, re-check your published prices before your first invoice, not after.

Which rate applies

• GST — 10%. Most goods and services sold or consumed in Australia.
• GST-free — 0%. Most basic food, many health and medical services, most education courses, childcare, and exports.

GST-free is not the same as input-taxed

Both mean the customer pays no GST, so they look identical from the buyer's side. For a seller they are entirely different, and the distinction decides whether you can reclaim tax on your costs:

• GST-free supplies carry GST at 0%. They count toward your registration threshold, they belong on your business activity statement (BAS), and you can claim back the GST on the costs of making them. Most basic food, many health and medical services, most education courses, childcare, and exports.
• Input-taxed supplies — residential rent, the sale of existing residential property, and most financial supplies — sit outside the system. You generally cannot claim back the GST on the costs behind them.
• Out of scope is a third category again, covering things like statutory fees and genuinely non-business activity.

A greengrocer selling GST-free food can register and claim back the tax on their van and their rent. A landlord or a lender making input-taxed supplies generally cannot. Same zero on the customer's bill, opposite consequences for the business.

Registering for GST, and the BAS

You must register once your GST turnover reaches $75,000 — gross business income minus any GST — measured on the current year or what you expect for it. You then have 21 days to register, and you need an ABN first. Taxi and ride-sourcing drivers must register from their first dollar, whatever their turnover.

• Registered businesses include GST in their prices and issue tax invoices showing their ABN.
• You claim GST credits for the GST included in business purchases, so what you pay the ATO is the GST you collected minus the credits.
• Both are reported on your business activity statement (BAS), usually quarterly for small businesses.

Retail prices in Australia are quoted GST-inclusive by law, which is why the reverse calculation — divide by 11 — is the one you will use most.

Where this fits with your other numbers

• Putting it on paper. A compliant invoice needs the net, the GST per rate, the gross and your ABN. Build one with the invoice generator rather than retyping the layout each time.
• What actually reaches you. GST passes through your business; your own income is what's left after it and after tax. If you pay yourself a salary, check your take-home pay so you are planning around the net figure rather than turnover.
• Set the money aside. The tax you collect is not yours to spend. Holding a quarter's worth in a separate account is the cheapest cash-flow discipline there is.

Tips and common mistakes

• Never subtract the rate from a gross figure. Divide by 1.10. The wrong method is off by $1.09 on $120.00 and scales with the amount.
• Split mixed receipts by rate. A supermarket total combining food and household goods cannot be unpicked with one division — the GST line on the receipt is the only reliable figure.
• Don't treat gross turnover as revenue. The tax element was never yours, and the return will ask for it whether you kept it or not.
• Round at the invoice, not at every step. Rounding each line to the penny then summing can leave you a penny or two off; that is normal and not worth chasing.
• Check the rate, not just the sum. The arithmetic is trivial; picking the wrong rate for a product is the error that actually costs money. When unsure, look it up with Australian Taxation Office (ATO).