GST Calculator

About Australian GST

GST (Goods and Services Tax) is a broad-based tax of 10% applied to most goods, services, and other items sold or consumed in Australia. Businesses with a GST turnover of $75,000 or more (or $150,000 for non-profit organisations) must register for GST with the ATO, charge it on taxable supplies, and lodge a Business Activity Statement (BAS). Once registered, you collect GST on sales (label 1A on the BAS) and claim credits on purchases (label 1B), with the net amount payable to or refundable from the ATO each quarter.

Not everything attracts GST. GST-free supplies include most basic food, medical services, and exports — these are taxed at 0%, meaning you can still claim input tax credits on related purchases. Input-taxed supplies (such as residential rent and most financial services) have no GST charged and no credits claimable on related costs. A common mistake is applying GST to a GST-free supply or forgetting to claim credits on a legitimate business expense — both errors flow directly into your BAS figures.

When extracting GST from a GST-inclusive amount, the correct formula is to divide by 11 — not multiply by 10%. For example, the GST in an AU$110 invoice is AU$10 (110 ÷ 11), not AU$11 (110 × 10%). This calculator handles that automatically in Remove GST mode. Always reconcile your GST accounts in Xero or MYOB to your BAS labels before lodging to catch any miscoded transactions.

How to use this GST calculator

1. Select Add GST if you have an ex-GST (net) amount and need to know the GST-inclusive price to put on your invoice.
2. Select Remove GST if you have a GST-inclusive amount (e.g. from a supplier invoice) and need to split it into the net amount and the GST component for your accounts.
3. Enter the dollar amount — results appear instantly showing gross, net, and GST.
4. Use the GST figure when coding the transaction in your accounting software, and reconcile it against your BAS at the end of each period.

Do I need to register for GST?

You must register if your annual GST turnover (gross income from sales subject to GST) is $75,000 or more. Turnover is assessed on a rolling 12-month basis — past or projected. Sole traders, companies, partnerships, and trusts all face the same threshold. Voluntary registration is available below $75,000 and can be beneficial if your customers are GST-registered businesses (as they can claim back the GST you charge).

What is the difference between Add GST and Remove GST?

Add GST takes a net (ex-GST) amount and calculates the GST-inclusive price: net × 1.1. Remove GST takes a gross (GST-inclusive) amount and extracts the GST component: gross ÷ 11. Confusing the two is a frequent bookkeeping error that leads to overstating or understating GST credits on the BAS.

Can I claim GST on all my business purchases?

You can claim input tax credits on purchases that are used for your business and are not GST-free or input-taxed. You also need a valid tax invoice from the supplier for amounts over $82.50 (including GST). For mixed-use purchases (partly personal, partly business), you can only claim the business portion. The ATO may audit GST credits, so keep supporting invoices for at least five years.

How often do I lodge a BAS and pay GST?

Most small businesses lodge quarterly, due on the 28th day after each quarter end (28 October, 28 February, 28 April, 28 July). Businesses with turnover over $20 million must lodge monthly. If you use a registered tax agent or BAS agent, you typically get an extended lodgement deadline. Late lodgement attracts a Failure to Lodge (FTL) penalty, and late payment accrues General Interest Charge (GIC) — currently around 11% per annum.