GST registration is one of those topics that looks simple on the surface but hides a surprising number of traps for clients who are growing fast, running multiple entities, or operating in specific industries. As a bookkeeper or accountant working with Australian small businesses, getting this right from the outset protects your clients from ATO penalties and, in some cases, from leaving money on the table.
The $75,000 Threshold: What It Actually Means
The current GST registration threshold sits at $75,000 in annual GST turnover for most businesses, and $150,000 for non-profit organisations. These figures have remained unchanged for several years and are regularly raised in industry consultations — but as of 2026, they remain the law.
The word "turnover" here is important. The ATO defines GST turnover as the gross value of taxable and GST-free supplies — not your client's profit, and not their net income after expenses. That means a business generating $80,000 in revenue but spending $60,000 to produce it still clears the threshold and must be registered.
Also critical: the test looks both backwards and forwards. A business must register if:
- Its current GST turnover (past 12 months) is at or above $75,000, or
- Its projected GST turnover (next 12 months) is likely to reach $75,000
The projected turnover test catches fast-growing startups that haven't crossed the line yet but are clearly heading there. If your client signs a large contract in April and their annualised revenue will exceed $75,000, they need to register before their next taxable supply — not at the end of the financial year.
Businesses That Must Register Regardless of Turnover
Some categories bypass the threshold entirely. Your clients must register for GST regardless of turnover if they:
- Provide taxi or rideshare services (this applies to Uber, DiDi, and similar platforms)
- Want to claim fuel tax credits
- Are a non-resident business making supplies connected with Australia
Rideshare is one that trips up new bookkeepers regularly. A driver earning $40,000 a year from a rideshare platform is required to be registered for GST and must lodge BAS — often quarterly. Missing this obligation means the ATO can assess GST on income already received, plus penalties and interest.
The Case for Voluntary Registration Below the Threshold
Here's where the conversation gets more nuanced. Voluntary registration is available to any business below the $75,000 threshold, and it can actually be advantageous in several situations:
Input tax credits on startup costs. A new business buying equipment, fit-out, vehicles, or professional services before reaching the threshold can claim back the GST component of those costs — but only if registered. For a client spending $50,000 on setup before their first dollar of revenue, that's potentially $4,545 in recoverable GST (GST = 1/11 of the GST-inclusive price).
B2B relationships. Many business clients require suppliers to provide a tax invoice with an ABN and GST details. If your client is selling to other businesses rather than consumers, being unregistered can raise questions about their credibility and prevent buyers from claiming input credits.
Consistent cash flow management. Some clients prefer the discipline of collecting and remitting GST from the start rather than facing a forced registration mid-year when records may already be messy.
The main downside of voluntary registration is the administrative obligation — typically quarterly BAS lodgement and the 21-day payment deadline — plus the requirement to stay registered for at least 12 months.
Registration Process and Timing
Once you've determined a client needs to register, they must do so within 21 days of the date they are required to be registered. Late registration doesn't eliminate the liability — the ATO can backdate GST obligations to the date the threshold was crossed, meaning your client may owe GST on supplies already made without having collected it.
Registration is handled through the Australian Business Register (ABR) or the ATO's online services. Clients with an existing ABN simply add GST to their registration; new businesses often do both simultaneously.
As a bookkeeper, it's good practice to set a turnover alert for clients approaching $60,000–$65,000 in annual revenue. That buffer gives you time to have the conversation, complete registration, and update their invoicing and accounting software templates before the threshold is crossed.
What Changes Once Registered
Once registered, your client's obligations shift:
- Charge GST on all taxable supplies (currently 10%)
- Issue tax invoices for sales over $82.50 (GST-inclusive)
- Lodge Business Activity Statements (monthly, quarterly, or annually depending on their turnover and ATO arrangement)
- Remit the net GST (GST collected minus input tax credits) by the due date
- Keep records for five years
One common error is clients continuing to quote prices exclusive of GST without updating their systems. If they were previously issuing invoices for $500 and suddenly add 10% on top, regular customers may push back — especially in consumer-facing industries.
Practical Advice for Your Practice
Build a GST registration review into your onboarding checklist for every new client engagement. Ask for the last 12 months of bank statements or accounting data and calculate their current GST turnover before assuming they're below the threshold.
For existing clients, a twice-yearly review — aligned with the June 30 and December 31 half-years — catches those approaching the threshold with enough lead time to act. Many bookkeepers use their reconciliation software's turnover reporting to flag clients automatically rather than relying on memory.
Finally, document your advice. If you've told a client they're below the threshold and recommended against voluntary registration, note the figures and the date. If their revenue spikes unexpectedly in the following months, that paper trail protects both of you.
Summary
The $75,000 GST threshold is straightforward in principle but full of edge cases in practice. Mandatory registration for rideshare, the forward-looking turnover test, and the compelling case for voluntary registration in some circumstances all require careful judgement. Stay close to your clients' revenue trajectory, build the registration review into your standard workflow, and you'll keep them compliant — and avoid the unpleasant surprise of an ATO audit revealing years of uncollected GST obligations.