There's a specific moment every growing tradie business hits. You check the numbers for the year, add it up, and realise you're closer to $75,000 than you thought. Then you spend the next twenty minutes googling "do I have to register for GST" at an hour of the night that is not ideal for reading tax legislation.
Good news: the answer is genuinely simple once you know it. Here's exactly when you have to register, when it's worth doing early anyway, and what actually changes the day you do.
The short answer
You must register for GST once your annual turnover reaches or is expected to reach $75,000 - registration is mandatory within 21 days of crossing that line. You can also register voluntarily below that threshold if it suits your business. Registration is free, done through the ATO, and once registered you must charge 10% GST on your invoices and lodge a BAS every quarter.
The $75,000 question, answered properly
The threshold is based on your GST turnover - your business income before expenses, calculated on a rolling 12-month basis, not a financial year. That distinction matters. It's not "did I earn $75k between 1 July and 30 June" - it's "does my last 12 months, or my next 12 months reasonably projected, add up to $75k or more."
Once you're at or expected to go over that line, registration isn't optional - the ATO requires you to register within 21 days of becoming aware you'll cross it.
Mandatory vs voluntary - which one is you?
| Situation | Registration status |
|---|---|
| Turnover already at or above $75,000 | Mandatory - register within 21 days |
| You reasonably expect to hit $75,000 in the next 12 months | Mandatory - same 21-day rule applies |
| Under $75,000, no immediate plans to grow | Optional - your call |
| Under $75,000 but doing regular commercial or B2B work | Optional, but often worth it early - see below |
What happens if you blow past the threshold and don't register
This is the part worth actually paying attention to, because the consequence is more annoying than most people expect.
If the ATO catches up with you after you've crossed the threshold without registering, they can register you retroactively - backdated to when you should have registered. That means you may owe GST on every sale from that date forward, whether or not you actually charged your clients for it at the time.
Read that again. You didn't collect the GST from your clients because you didn't know you needed to. The ATO still wants it. Which means it comes straight out of your own margin instead of being collected along the way, the way it's supposed to work. It's one of those tax situations where being a few months late to notice can turn into a genuinely expensive lesson.
Why some tradies register early, on purpose
Registering before you're forced to isn't just for tradies chasing compliance gold stars. There are real, practical upsides:
- GST credits from day one. Once registered, you can claim back the GST on tools, materials, fuel, and vehicle costs - which for a tradie buying gear regularly can add up to a meaningful amount.
- Commercial credibility. Some builders, principal contractors, and larger commercial clients prefer or expect to deal with GST-registered suppliers - it simplifies their own GST reporting.
- No scramble later. You set up your invoicing and pricing for GST once, calmly, instead of retrofitting it under pressure the moment you cross the threshold mid-job.
The trade-off: you then need to charge GST on everything and lodge a quarterly BAS, even while your turnover is still modest. For a tradie doing plenty of materials-heavy work, the GST credits alone often make this a wash or a net win. For a tradie doing mostly small, low-materials jobs, it may not be worth the extra admin yet.
How to actually register - the steps
- Make sure you already have an ABN - see do tradies need an ABN if you haven't sorted this yet, since GST registration links to it.
- Log into the ATO's Business Portal or myGov with your ABN linked.
- Select "Register for GST" and confirm your details, expected turnover, and the date you want registration to start from.
- Choose your reporting cycle - quarterly is standard for most tradies, though monthly and annual options exist depending on your turnover.
- Registration is usually confirmed quickly, often the same day for straightforward applications.
It costs nothing to register. The only cost is the admin that comes with it afterward - which, done properly, is a quarterly 30-minute job, not a quarterly crisis.
What changes on your invoices the day you register
This is the part that trips people up if they don't prepare for it. Once registered, every invoice for a taxable sale of $82.50 or more legally needs:
| Field | What changes |
|---|---|
| Document heading | Must say "Tax Invoice", not just "Invoice" |
| ABN | Must appear on the invoice |
| GST amount | Shown separately, or a clear statement that GST is included in the total |
| Total price | Now includes the 10% GST component |
For the full detail on getting every field right, see how to write a tax invoice as a tradie. Update your invoice template before your first post-registration invoice goes out - not after a client's accountant sends it back.
Telling clients your prices are changing
This is the conversation most tradies dread and it's genuinely a non-event if you handle it upfront instead of letting it show up as a surprise on an invoice.
Something like: "Just a heads up, I've registered for GST as the business has grown, so from [date] my invoices will include 10% GST on top of what we've been working with."
Most reasonable clients understand this as a normal sign a business is growing. What causes friction is a client opening an invoice that's suddenly 10% more than the last one with zero warning and no explanation. Same price change, completely different experience depending on whether you said something first.
What about GST you've already collected informally?
If you've been quietly adding 10% to your prices before you were actually registered - which happens more often than you'd think, usually from confusion rather than anything deliberate - stop and get this straightened out properly. You can't remit GST to the ATO without being registered, and charging it without being registered isn't compliant either way. Register properly, set your official start date, and make sure your pricing and invoicing align with that date going forward. If you're unsure how far back this goes, a quick conversation with an accountant is worth the hour.
The one-line version to remember
$75,000 rolling turnover is the line. Cross it, or expect to, and you've got 21 days to register. Below it, it's your call - and for a tradie buying materials regularly or chasing commercial work, registering early is often worth doing on purpose rather than waiting to be forced into it.
Frequently asked questions
What happens if I go over $75,000 and don't register for GST?
You're required to register within 21 days of crossing the threshold, or once you reasonably expect to. If you don't, the ATO can register you retroactively, and you may owe GST on sales made after that date - even if you never charged your clients for it, meaning it comes straight out of your own pocket.
Can I register for GST before I hit $75,000?
Yes, voluntarily, at any turnover. Many tradies do this early to claim GST credits on tools, materials, and vehicle costs from day one, and because some commercial clients prefer GST-registered suppliers. The trade-off is charging GST on everything and lodging a quarterly BAS while turnover is still small.
How do I tell existing clients my prices are changing because of GST?
Be upfront and specific, ideally before your next invoice rather than as a surprise. Explain you've registered as the business has grown and prices will now include 10% GST from a stated date. Most clients understand this as a normal part of growth - it's a far easier conversation had ahead of time than discovered on an invoice.
Do I need new invoice templates after registering for GST?
Yes. Every invoice for a taxable sale of $82.50 or more must say "Tax Invoice", include your ABN, show the GST amount or state it's included, and show the total including GST. Update your template before your first post-registration invoice goes out.