ABN Check: Validate an ABN or ACN Check Digit
An ABN has 11 digits and a weighted sum divisible by 89 after subtracting 1 from its first digit. An ACN has 9 digits with a different check-digit rule. Enter either number to test its arithmetic format, preserving any initial zeroes. A passing result does not confirm registration, trading status or GST registration; check the entity on ABN Lookup.
ABN check-digit result
Yes
Show breakdown
Calculation breakdown
- Valid
- Yes
| Valid | Yes |
|---|
ABN validation checks the check digit only. It does not confirm registration or GST status. Confirm the entity on ABN Lookup.
At a glance
- Required on a tax invoice
- Tax invoice wording, seller identity and ABN, date, quantity and price, GST amount and taxable status
- Sales of $1,000 or more
- the buyer's identity or ABN must also appear
- Note
- Tax invoices are required for sales over $82.50 including GST when the buyer asks
- GST
- 10% per taxable line; GST-free lines shown separately
- ABN check
- 11 digits, weighted sum divisible by 89 (this confirms the format, not the registration)
- Not registered for GST
- issue an "Invoice", not a "Tax invoice", with no GST
- Note
- Nothing you type leaves your browser; details can be remembered on this device only
How it is calculated
Round each discounted line amount to cents, apply GST to taxable lines and add the totals. Check the ABN or ACN algorithm separately from the document requirements.
line_amount_ex = round2(qty × unit_price × (1 − discount))
line_gst = round2(line_amount_ex × 10%) if GST applies else 0
subtotal = Σ line_amount_ex
gst_total = Σ line_gst (line rounding)
= round2(Σ taxable line_amount_ex × 10%) (total rounding)
total = subtotal + gst_total
ABN check: strip spaces; 11 digits; subtract 1 from the first digit; weights 10,1,3,5,7,9,11,13,15,17,19; sum mod 89 = 0
ACN check: 9 digits; weights 8,7,6,5,4,3,2,1 on the first 8; check digit = (10 − sum mod 10) mod 10 equals the 9th
Tax invoice requirements (ATO), checked live and shown as a checklist:
"Tax invoice" words · seller identity · seller ABN · date · description of items (qty and price) · GST amount shown, or "total price includes GST" when every line is taxable
· if total ≥ $1,000: buyer's identity or ABN · if some lines are GST-free: GST shown per line or the taxable lines markedWhat is the difference between an ABN and an ACN?
An Australian Business Number identifies an entity for business and tax dealings, while an Australian Company Number identifies a registered company. ABNs have eleven digits and ACNs have nine, with different check-digit algorithms. A company may have both; other entities may have only an ABN.
Can a cancelled ABN still pass the check-digit test?
Yes. Cancellation does not change the digits, so the number can remain mathematically valid after its registration status changes. Use the official ABN Lookup register to check the entity name, current status and GST registration before relying on a supplier’s details.
What must a tax invoice include in Australia?
The ATO sets seven requirements for a tax invoice for sales under $1,000: it must be intended to be a tax invoice (usually by carrying the words “Tax invoice”), show the seller’s identity and ABN, the date it was issued, a brief description of each item sold including quantity and price, the GST amount payable (or a statement that the total includes GST when every item is taxable at 10%), and the extent to which each sale is taxable when some items are GST-free. For sales of $1,000 or more it must also show the buyer’s identity or ABN. If any of these is missing the buyer cannot claim the GST credit until a valid invoice is issued, which is the most common reason a customer sends an invoice back. The generator shows the checklist beside the document and ticks each item as the form is completed.
How do you check an ABN is valid?
An Australian Business Number has 11 digits and a built-in check: subtract 1 from the first digit, multiply each digit by its weighting (10, 1, 3, 5, 7, 9, 11, 13, 15, 17, 19), add the results, and the total is divisible by 89 for a valid number. The generator runs that test as you type and flags a transposition or typo immediately, which catches most errors before the invoice goes out. It does not confirm the business exists or is registered for GST; for that, search ABN Lookup, which also shows the entity’s registered name and GST status, both worth checking before you pay a new supplier or extend credit to a new customer.
Should you charge GST on every line?
Only on taxable lines. A registered business charges 10% GST on most goods and services, but GST-free items (most basic food, some medical and educational supplies, exports) and input-taxed items carry none, so an invoice with mixed lines shows the GST per line and the total GST, and a GST-free line is marked as such. GST is rounded to the nearest cent, either line by line or on the taxable total, and the generator lets you choose. A business not registered for GST must not charge it and must not call the document a tax invoice; switch off “Registered for GST” and the generator produces a plain invoice with no GST column.
When does a business outgrow generating invoices by hand?
When the same customer, product and price details are typed into every document, when quotes turn into invoices by retyping, when stock is not reduced by the sale, and when the BAS is assembled from a folder of PDFs. Accounting software fixes the first two; the step after that is a system where the product record carries the price and tax code, a quote becomes an order becomes an invoice becomes a stock movement and a ledger entry without re-entry, and the ATO’s requirements are enforced on every document by design. That is the point at which we usually meet a wholesaler, and it is what moving from Xero or AccountRight to an ERP means in practice.
| Line | Qty | Unit price ex GST | Amount ex GST | GST | Amount inc GST |
|---|---|---|---|---|---|
| Consulting day | 3 | $199.00 | $597.00 | $59.70 | $656.70 |
| GST-free export item | 2 | $45.00 | $90.00 | $0.00 | $90.00 |
| Widget | 7 | $3.33 | $23.31 | $2.33 | $25.64 |
| Subtotal ex GST | $710.31 | ||||
| GST | $62.03 | ||||
| Total inc GST | $772.34 | ||||
| Compliance | Tax invoice required (over $82.50); buyer identity not required (total under $1,000) |
Frequently asked questions
What is the difference between an ABN and an ACN?
An Australian Business Number identifies an entity for business and tax dealings, while an Australian Company Number identifies a registered company. ABNs have eleven digits and ACNs have nine, with different check-digit algorithms. A company may have both; other entities may have only an ABN.
Can a cancelled ABN still pass the check-digit test?
Yes. Cancellation does not change the digits, so the number can remain mathematically valid after its registration status changes. Use the official ABN Lookup register to check the entity name, current status and GST registration before relying on a supplier’s details.
Do I need to be registered for GST to issue an invoice?
No. Any business can issue an invoice, but only a GST-registered business can issue a tax invoice and charge GST. If you are not registered, the document is an "Invoice", it shows no GST, and it should state that no GST has been charged. Registration is compulsory at $75,000 turnover.
Is a tax invoice required for every sale?
A tax invoice must be provided within 28 days when a customer asks for one and the sale is more than $82.50 including GST. Below that, a receipt or a simpler document is enough for the buyer to claim the credit. Most businesses issue tax invoices for every sale regardless, which the generator supports.
moving from Xero or AccountRight to an ERP
If quotes, orders, invoices and stock are four separate steps in your business, an ERP makes them one. Talk to us about what that looks like for your volume.
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