ABN & ACN Checker (Australia)

ABN & ACN Checker tests the numbers Australian businesses and payroll teams deal with every day: the 11-digit Australian Business Number, the 9-digit Australian Company Number, the Australian Registered Body Number used by foreign companies and other registered bodies, and the tax file number. Each one ends in, or is built around, check digits worked out with a fixed formula, so a single mistyped or swapped digit almost always shows up.

Type or paste a number and it is grouped the way it is printed (51 824 753 556) while you type. You get a clear pass or fail, the reason in plain words, such as “wrong length” or “the last digit should be 9”, and the full working: each digit, its weight, the products, the total and the remainder. If you enter an ACN, it shows the ABN that company would have, because the ATO builds company ABNs from the ACN. A list tab checks thousands of numbers at once and saves the results as a spreadsheet file.

Two honest limits. It only knows the formula, not the register: a pass means the number could exist, not that the business is real or still trading, so confirm important ones on the government’s ABN Lookup. And it is for Australian numbers only. Nothing you type leaves your device, which matters most for tax file numbers.

1. Choose ABN, ACN, ARBN or TFN at the top of “Check one number”.
2. Type or paste the number. Spaces, dashes and dots are ignored, and the result updates as you type.
3. Read the verdict and reason, then “The maths, step by step” to see where a bad number goes wrong.
4. For many numbers, open “Check a list”, paste one per line, and pick how 9-digit numbers should be read.
5. Press “Download CSV” to save the results, or “Copy formatted” to copy a single number with the usual spacing.

• Four number types: ABN (modulus 89), ACN and ARBN (modulus 10 check digit) and TFN (modulus 11, including older 8-digit numbers).
• Automatic grouping as you type, with the cursor kept in place when you edit the middle of a number.
• A plain reason for every failure: wrong length, a leading zero on an ABN, a wrong check digit or a non-zero remainder.
• A digit-by-weight table and numbered working lines, ready to copy into a support ticket or a lesson.
• ABN and ACN cross-check: an ACN shows its matching company ABN, and an ABN that contains a valid ACN is flagged as probably a company.
• List mode for up to 5,000 numbers, separated by lines, commas, semicolons or tabs, with a valid and failed count.
• CSV export that opens cleanly in Excel, Numbers and Google Sheets, keeping leading zeros.

• Before paying an invoice from a new supplier, run the ABN here, then look it up on ABN Lookup to check the name and whether it is registered for GST.
• A swapped pair of digits is the most common typing error, and the ABN formula catches nearly all of them. If a number fails, compare it with the original pair by pair.
• When cleaning a customer list, choose “ACN” or “TFN” under “Read 9-digit numbers as” to match what the column holds. The tool can’t tell them apart from the digits alone.
• Only collect or record tax file numbers if the law lets you. This checker won’t store them, but your spreadsheet will.