How do I work out the GST in a price that already includes it?

Divide the total by 11. A $891 invoice contains $81 of GST and $810 before GST. Dividing by 1.1 gives you the ex-GST price directly.

Is GST 10% of the total or 10% of the ex-GST price?

10% of the ex-GST price. That is why it works out to one eleventh of the GST-inclusive total rather than one tenth of it.

What if some lines on my invoice are GST-free?

GST applies line by line, not to the whole document. Calculate GST only on the taxable lines and total them separately. The Docketlane editors handle mixed GST and GST-free lines on the same invoice.

Can I charge GST before my registration is active?

No. GST applies from your registration date. If you register later and want to charge GST on work already done, the date your registration takes effect is what governs it, and backdating has rules of its own.

Do I round GST up or down?

Calculate GST on each line, then total. Rounding each line to the nearest cent and summing is the normal approach, and it is what keeps a document's GST total consistent with its line items. Docketlane calculates in cents to avoid rounding drift.

Is this the same as a tax invoice?

No. A calculation tells you the number; a tax invoice is a document with required content — your identity, your ABN, the date, what you supplied, and the GST. Use the invoice generator to produce one.

Free Australian calculator

Australian GST calculator

Enter a GST-exclusive or GST-inclusive amount to see the price before GST, the GST component and the total including GST.

Add 10% GST to an exclusive amount
Extract the 1/11 GST component from an inclusive amount
Continue into an invoice or quote

Calculate Australian GST

Docketlane is a drafting tool, not tax or legal advice.

The mistake that costs you 91 cents in every dollar of GST

Taking 10% off a GST-inclusive price does not give you the price before GST. Try it: $110 minus 10% is $99, but the ex-GST price is $100. The 10% was added to the smaller number, so removing it has to work backwards.

The rule worth memorising is divide by 11. The GST inside any GST-inclusive Australian price is that price ÷ 11. On $110 that is $10. On $1,320 it is $120. The calculator above does it either direction, but on a job site with a phone in one hand, divide by 11 is the one to keep.

What you know	To get the other numbers	Example
Price before GST	× 1.1 for the total, × 0.1 for the GST	$500 → $50 GST → $550 total
Price including GST	÷ 11 for the GST, ÷ 1.1 for the ex-GST price	$550 → $50 GST → $500 ex-GST
GST amount	× 10 for the ex-GST price, × 11 for the total	$50 → $500 ex-GST → $550 total

The same job, priced three ways

Quote in whichever direction your customer thinks in. Homeowners almost always hear the total, so a quote of "$550 all up" reads as honest where "$500 plus GST" reads as a surprise coming. Builders and businesses usually work ex-GST, because they claim the GST back.

Do you have to charge GST at all?

Only if you are registered for GST. Registration is compulsory once your GST turnover reaches A$75,000 in a 12-month period — that is turnover, not profit, and it looks forward as well as back: if you can see the next twelve months crossing the line, you are meant to register within 21 days of that becoming clear.

A$75,000 — the threshold for most sole traders and businesses.
A$150,000 — the threshold for non-profit organisations.
No threshold at all — taxi, limousine and ride-sourcing drivers must register from the first fare.
Voluntary registration is allowed under the threshold, and can be worth it if you buy a lot of GST-bearing tools and materials, because you can claim that GST back.

Not registered? Then your document is an invoice, not a tax invoice, and it must not show a GST line or the words "tax invoice". Charging GST you are not registered to collect is the kind of error that surfaces at the worst possible time. The tax invoice checker tests a finished document against the requirements before you send it.

Registered? Then GST applies to most of what you sell, but not everything. Basic food, most medical and health services, and some education and childcare are GST-free. Residential rent and most financial supplies are input-taxed, which means no GST on the sale and no credit on the purchases behind it.

Where the GST you charge actually goes

The GST on your invoice is never your money. You collect it, hold it, and hand it over on your business activity statement. What you send the ATO is the GST you collected on sales minus the GST you paid on business purchases — the second half is the one people forget, and it is real money back.

Quarter	Covers	Usually due
Q1	July – September	28 October
Q2	October – December	28 February
Q3	January – March	28 April
Q4	April – June	28 July

Standard quarterly BAS periods

Quarter 2 gets the extra month because of Christmas. Lodging through a registered BAS or tax agent can shift some of these dates, and businesses over A$20 million turnover report monthly.

The practical habit: move the GST out of the account it landed in. A separate account that only ever receives the GST portion of each payment turns BAS day from a shock into a transfer. In Docketlane, the BAS report totals GST on your sales and GST on your recorded expenses for the quarter you choose, so both halves come from the same place.

Common questions

How do I work out the GST in a price that already includes it?: Divide the total by 11. A $891 invoice contains $81 of GST and $810 before GST. Dividing by 1.1 gives you the ex-GST price directly.
Is GST 10% of the total or 10% of the ex-GST price?: 10% of the ex-GST price. That is why it works out to one eleventh of the GST-inclusive total rather than one tenth of it.
What if some lines on my invoice are GST-free?: GST applies line by line, not to the whole document. Calculate GST only on the taxable lines and total them separately. The Docketlane editors handle mixed GST and GST-free lines on the same invoice.
Can I charge GST before my registration is active?: No. GST applies from your registration date. If you register later and want to charge GST on work already done, the date your registration takes effect is what governs it, and backdating has rules of its own.
Do I round GST up or down?: Calculate GST on each line, then total. Rounding each line to the nearest cent and summing is the normal approach, and it is what keeps a document's GST total consistent with its line items. Docketlane calculates in cents to avoid rounding drift.
Is this the same as a tax invoice?: No. A calculation tells you the number; a tax invoice is a document with required content — your identity, your ABN, the date, what you supplied, and the GST. Use the invoice generator to produce one.