GST registration attaches to the entity, the ABN, not to each business name. Run two ventures as the same sole trader or company and their turnovers are added together against the one $75,000 threshold; once registered, GST applies to every taxable sale the entity makes, both ventures included. Separate legal entities, by contrast, each get their own ABN and their own threshold.
Register for GST →5-minute form · usually done in 4 business hours
One ABN, one threshold, one registration.
Say you're a sole trader doing $50,000 of graphic design and $30,000 of weekend market sales. Neither venture alone crosses $75,000, but the entity (you) is at $80,000, and the 21-day clock starts. Registration then covers the whole ABN: you can't charge GST on design invoices but not market stall sales. One BAS reports the lot, too: internal bookkeeping can split the ventures, but the ATO sees one taxpayer. (More on how ABN and GST fit together.)
"Can I keep one business out of it?"
Not under the same ABN. The only way a venture gets its own threshold is to sit in a genuinely separate entity, a company or trust with its own ABN. That's a real structural decision with real costs (set-up, accounting, separate BAS if registered) and it needs a commercial reason: splitting a single business purely to stay under the GST threshold is the kind of arrangement anti-avoidance rules exist for. If the structure question is live, that's an accountant conversation, not a form.
Hobbies don't count.
GST turnover counts business income. A genuine hobby (no profit motive, no business-like organisation) isn't an enterprise, and its income doesn't push you toward the threshold. The line matters and the ATO looks at substance: regular sales, marketing, and profit intent all point to "business", however it started.
The opposite case: GST grouping.
Related entities that want to be treated as one (common in company/trust structures under shared ownership) can form a GST group: one BAS for the group, and transactions between members ignored for GST. It's the mirror image of the splitting question and only relevant once you genuinely run multiple entities.
Quick answers.
Can I have two ABNs as a sole trader so each business gets its own threshold?
No. An individual gets one sole-trader ABN, full stop. A second ABN means a second entity (a company, trust or partnership), which is a real structural change with its own costs and obligations.
Once registered, do I charge GST in both businesses?
Yes: registration covers the entity, so every taxable sale under that ABN carries GST, whichever venture made it. Pricing in the smaller venture needs updating the day you register.
Does hobby income count toward the $75,000?
No, genuine hobby income isn't enterprise turnover. But the ATO judges substance over labels: regular, organised, profit-seeking activity is a business no matter what you call it.
A new venture will push me over $75,000: when do I register?
Within 21 days of when your combined expected 12-month turnover crosses the line, not at year end. If you're near the line and growing, registering at the start of the new venture is usually cleaner than backdating later.
Related guides: ABN and GST: how they fit · Do I need to register for GST? · Crossing the $75,000 threshold
Two ventures, one registration. Done in ~4 business hours.
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