The Australian Business Number (ABN) is the 11-digit identifier issued by the Australian Business Register (ABR) to entities carrying on an enterprise in Australia. For bookkeepers, the ABN sits at the centre of several compliance obligations — most critically, the requirement to withhold 47% of any payment to a supplier who fails to quote an ABN. Understanding the registration rules, the withholding obligations, and the update and cancellation processes protects both your clients and the businesses they deal with.
Who Must Register for an ABN
Under the A New Tax System (Australian Business Number) Act 1999, an entity is entitled to an ABN if it is carrying on an enterprise in Australia. An enterprise is broadly defined under the GST Act to include any activity done in the form of a business, or as a regular or continuous activity in the form of a lease, licence, or other grant of an interest in property.
Entities entitled to register include:
- Companies, partnerships, trusts, and joint ventures carrying on business
- Sole traders operating a business
- Not-for-profit organisations and charities (even if not operating for profit)
- Government entities
Individuals who are employees only — with no business activities, no investment property, no ABN-requiring side work — are not entitled to an ABN. The ABR has processes to cancel ABNs that were incorrectly granted, and the ATO actively reviews ABN entitlement as part of its shadow economy compliance work.
The practical test for a sole trader client is whether they are genuinely running a business: is there intention to make profit? Is the activity repeated and systematic? Is there a business structure, clients, and invoices? If yes, the ABN is legitimate and should be registered before any invoicing commences.
The 47% No-ABN Withholding Rule
The no-ABN withholding obligation is one of the most practically significant ABN rules for bookkeepers managing client payments. Under Division 12 of the Taxation Administration Act 1953 (TAA 1953), a payer is required to withhold 47% (the top marginal tax rate) from a payment to a supplier if the supplier:
- Does not quote an ABN on their invoice or request for payment, and
- The payment is for a business-to-business supply (i.e., the supplier is not an employee, and the payment is made in the course of an enterprise)
The withheld amount must be remitted to the ATO as PAYG withholding — it cannot be retained by the payer as income. The payer must issue a payment summary or incorporate the withholding into their PAYG W reporting through Single Touch Payroll or the PAYG withholding annual report.
Exceptions to the withholding obligation include:
- Payments of $75 or less (the de minimis threshold)
- Payments to suppliers who are not carrying on an enterprise (e.g., a one-off private sale of personal goods)
- Payments covered by a valid voluntary agreement (the supplier is effectively treated as an employee for PAYG purposes)
- Supplies made through certain financial institutions where the ABN details are verified through the institution
For clients who regularly engage contractors, subcontractors, or freelancers, the no-ABN withholding rule creates a practical obligation: always collect an ABN before processing payment. The bookkeeper's accounts payable process should include ABN verification as a mandatory step on every new supplier setup. The ABR provides a free ABN Lookup tool (abr.business.gov.au) that allows real-time verification.
Where a supplier provides an ABN but it cannot be verified on the ABR (because it has been cancelled, or was never valid), the payer is not protected from the withholding obligation. Verification at the time of the first payment — not just at supplier setup — is best practice.
Bookkeeping Treatment of No-ABN Withholding
When a client pays a no-ABN supplier and withholds 47%, the bookkeeping treatment is:
- Code the full invoice amount as the expense (e.g., $1,000 subcontractor services)
- Credit the bank account for the net payment made (e.g., $530 — which is $1,000 × 53%)
- Credit a PAYG withholding liability account for the withheld amount ($470)
- When the withheld amount is remitted to the ATO, debit the PAYG withholding liability and credit the bank account
The supplier's expense is still the full $1,000 — the withholding is not an additional cost to the payer; it is part of the payment that is redirected to the ATO. The supplier can claim the withheld amount as a credit on their own tax return.
In practice, most clients find the no-ABN withholding process administratively burdensome and prefer to simply require suppliers to provide an ABN before any payment is made. This is the cleaner outcome.
Updating ABN Details
Registered entities are legally required to update their ABN details within 28 days of a change in any registered information. This obligation is often overlooked by small business clients. Key changes that trigger an update requirement include:
- Change of business name (including cessation of a trading name)
- Change of business address
- Change in the main business activity (industry code)
- Change of officeholders, partners, or trustees
- Addition or removal of a business location
- Change from GST-registered to not GST-registered (or vice versa)
GST registration and de-registration are managed through the ABR but have direct ATO implications — a client who de-registers for GST while still making taxable supplies above the $75,000 threshold is committing a compliance failure. Similarly, a client who cancels their ABN while still operating creates problems for their own invoicing and for suppliers who may then be required to withhold from future payments to them.
Encourage clients to review their ABN registration details annually — as a part of the EOFY checklist is a natural time — and to notify you of any structural changes (new business name, change of address, new partners) so the ABR update can be made within the 28-day window.
Cancelling an ABN
When a client ceases to carry on an enterprise, the ABN should be cancelled. Continuing to hold an ABN after ceasing business is not itself an offence, but it creates risks:
- Third parties may continue to deal with the ABN as if the business is active
- The ATO may issue compliance queries or notices expecting lodgements that are no longer relevant
- State revenue authorities may continue to expect payroll tax lodgements
To cancel an ABN, the entity's authorised contact logs into the ABR and selects the cancellation option, providing the date on which the enterprise ceased. The cancellation is effective from that date, not the date of the notification.
Where a client is closing a company (rather than a sole trader or partnership), the company must go through formal deregistration with the Australian Securities and Investments Commission (ASIC) under the Corporations Act 2001 in addition to cancelling the ABN. Company deregistration and ABN cancellation are separate processes — completing one does not automatically complete the other.
For bookkeepers, the practical takeaway is to include ABN cancellation on the final client offboarding checklist, alongside final BAS lodgement, payroll finalisation, and asset disposal. Leaving a cancelled business's ABN active is a loose end that occasionally creates downstream compliance issues.