Crossing the $75,000 GST threshold: the 21-day rule and what it costs to miss it

Most businesses meet GST as a number on a page: $75,000. What that number does not tell you is that it works on a rolling twelve months rather than a financial year, that you get 21 days once you cross it, and that registering late makes you liable for GST on sales where you never charged any.

That last part is what turns a paperwork issue into a real bill. Here is how the whole thing actually works.

How the threshold is measured

GST turnover is your gross business income, excluding GST itself, input-taxed sales, sales that are not for payment, and sales not connected with Australia. It is not profit, and it is not your bank balance.

You must register if either of these is true:

• Current GST turnover - this month plus the previous 11 - is $75,000 or more; or
• Projected GST turnover - this month plus the next 11 - is $75,000 or more.

Two things follow from that, and both catch people.

First, it is a rolling twelve months, not a financial year. Turnover does not reset on 1 July. A business that does $30,000 between January and June and $50,000 between July and December has crossed, even though neither financial year on its own looks close.

Second, projected turnover means you can be required to register before you have actually earned $75,000. Sign a contract in August that will clearly take you past the line over the following twelve months, and the obligation starts then - not when the money lands.

Different thresholds

• Non-profit organisations: $150,000.
• Taxi, limousine and ride-sourcing drivers: no threshold at all. You must be registered from your first fare, whatever you earn.

The 21-day rule, and why it matters more than the threshold

Once your GST turnover reaches the threshold, you have 21 days to register.

The part that costs money is what happens if you do not. Your registration takes effect from the date you crossed the threshold, not the date you got around to applying. The ATO can backdate it - up to four years, absent fraud.

Work through what that means. If you crossed in March and register in November, you are treated as having been registered since March. Every taxable sale in between now carries GST that you owe the ATO. You did not charge it, because you did not know you had to. The ATO does not care: one-eleventh of those sales comes out of margin you have already spent, plus interest, plus potential penalties.

There is one consolation. Backdated registration also entitles you to backdated GST credits on your purchases across the same period - which is exactly why keeping your tax invoices matters even before you are registered.

The practical version: watch the rolling twelve-month figure monthly, not at year end. In Xero this is a report, not a calculation - and it is the single most useful thing to look at in a growing business's first two years.

What actually changes on registration

You charge 10% more

GST applies to most goods and services sold in Australia. Some things are GST-free - most basic food, most medical and health services, most education - and getting that classification right is worth checking rather than assuming.

The commercial question is who absorbs the 10%. If your customers are GST-registered businesses, they claim the credit and are genuinely indifferent to the increase. If your customers are consumers, a 10% rise is a 10% rise, and the choice is between a price increase and a margin cut. Decide that deliberately before you register, not in the middle of the first quarter.

You claim GST back

Every business purchase carrying GST now generates a credit. For a business with real input costs - stock, materials, equipment, subcontractors - this is significant, and it is why some businesses register voluntarily below the threshold.

You need a valid tax invoice for anything over $82.50 including GST, and the claim has to be made within four years. To pull the GST out of a tax-inclusive figure, divide by 11 rather than taking 10% off - our GST calculator does it both ways if you would rather not do it in your head.

You lodge a BAS

Quarterly for most businesses. Monthly if turnover is $20 million or more, or if you choose it. Annually if you registered voluntarily and are still under $75,000.

The BAS is where you report GST collected, subtract GST paid, and remit the difference. Which brings us to the thing that catches more newly-registered businesses than anything else.

The cash flow trap

The GST you collect is not your money. It arrives in your bank account, sits there alongside everything else, looks exactly like revenue, and three months later has to be paid to the ATO.

A business turning over $300,000 collects roughly $30,000 of GST a year. Spend it as it comes in - which is very easy to do, because it is genuinely indistinguishable from income in your account - and the quarterly BAS arrives as a bill you have no money for. This is the origin story of a large share of ATO payment plans.

The fix is boring and it works: a separate account, and a standing transfer of the GST component out of the operating account as sales land. Some businesses do it weekly, some monthly. What matters is that it happens without a decision each time.

Should you register early?

Below the threshold it is optional, and worth thinking about rather than defaulting to no.

Arguments for: if you have significant GST-bearing costs, you get those credits back. If you sell to businesses, they are indifferent to your price rising 10% because they claim it. And some larger clients and government buyers have procurement systems that assume every supplier is registered - not being registered can quietly take you off the list.

Arguments against: if you sell to consumers and your costs are mostly your own labour, registration means a 10% price rise or a 10% margin cut, plus quarterly lodgements, for very little credit coming back.

The pattern is straightforward. Business-to-business with real input costs: register early. Consumer-facing service business with low inputs: wait until you have to.

Registering

You need an ABN first - GST registration attaches to it. If you do not have one, you can apply for both together through the Australian Business Register.

From there you have three options, and they suit different people:

• Do it yourself, free, through ATO online services for business. Fine if you have an ABN, a myGovID and twenty minutes.
• Have it done for you. We also run GST Register, where a one-page form is reviewed by a registered agent and most registrations are completed within a couple of business hours. There is a fee for that, and it exists because a meaningful number of people would rather not deal with ATO online services at all.
• Ask your BAS or tax agent to handle it as part of what they already do for you. If we do your books, this is simply included.

Where we come in

Crossing the threshold is the point where bookkeeping stops being optional. It is not the registration that is difficult - it is what follows: correct GST coding on every transaction, valid tax invoices, quarterly lodgement on time, and the cash actually being there when the BAS falls due.

That is what we do. We are a registered BAS agent, we set the Xero file up so the coding is right from the start, and we tell you what the quarter looks like before it arrives rather than after.

If you are approaching $75,000 or have just realised you went past it a while ago, have a conversation with us - the second one is far more common than people think, and far more fixable than it feels.

General information only, current as at the date above, and not advice on your own circumstances. Confirm current thresholds and obligations with the ATO or your adviser.