Australian identifier validation (TFN, ABN, ACN)
Overview. When you collect an Australian identifier on an IdentityCheck form, the platform checks that the number is well-formed and passes its built-in check digit before the form is accepted. This applies to the Tax File Number (TFN), Australian Business Number (ABN), Australian Company Number (ACN) and UK Unique Taxpayer Reference (UTR). A typo or a made-up number is caught with a clear error at submission, so bad data does not reach your records.
Does it validate ABNs, TFNs and other identifiers?
Yes. Australian identifiers are not random strings of digits; each is constructed with a mathematical check digit so that computers can detect common data-entry mistakes. IdentityCheck validates each identifier by question type:
- TFN (Tax File Number). 9 digits with the ATO checksum.
- ABN (Australian Business Number). 11 digits with its checksum.
- ACN (Australian Company Number). 9 digits with its check digit.
- UTR (Unique Taxpayer Reference). The UK identifier, for firms with cross-border clients.
You set the identifier type when you add the question in the form builder. From then on, any answer to that question is validated automatically. There is nothing for the client to configure and nothing extra for you to switch on.
How does it stop bad TFN entry?
The check happens the moment a client tries to submit the form. If the number does not satisfy its checksum, the form highlights that field with a plain-English error and holds the submission until the number is corrected. Because changing or swapping a single digit almost always breaks the check digit, the great majority of accidental typos are caught right there, at the point of entry.
This matters because a bad identifier is expensive to fix later. A transposed digit in a TFN or ABN can quietly flow into your practice records, your correspondence and your lodgements, and only surface as a problem weeks later. Catching it at submission keeps your client records clean from the start and saves you the chase to get the correct number afterwards.
One important boundary: a valid checksum confirms the number is properly formed, not that it belongs to the person or entity in front of you. Validation is a data-quality safeguard, not a substitute for confirming identity and ownership as part of your due-diligence process.
What if a client does not have a TFN?
Some clients, such as non-residents, do not have a Tax File Number. If your form makes the TFN question mandatory, ask them to enter 000 000 000. This is the ATO's standard code for a TFN that has not been quoted, and it passes the form's check, so the client can submit.
Other placeholders, such as 999 999 999, fail the checksum and the form will not accept them. When a client uses 000 000 000, note on their record that no TFN was provided, so your team knows the field is intentionally blank.
Frequently asked
Does IdentityCheck check that an ABN or TFN is valid? It validates the format and checksum of the number. Australian identifiers such as the TFN, ABN, ACN and UTR are built with a mathematical check digit, and IdentityCheck confirms the number satisfies that check before accepting the form. This catches mistyped and made-up numbers at the point of entry.
What happens if a client mistypes their TFN? The form shows a clear error on that field and will not accept the submission until the number is corrected. Because a single transposed or wrong digit breaks the checksum, most typos are caught immediately, rather than surfacing later when you try to use the number.
Does a valid checksum mean the number really belongs to that person? No. A checksum confirms the number is well-formed and internally consistent, not that it is registered to that individual or entity. It is a data-quality safeguard that reduces errors in your records. Confirming ownership is part of your wider due-diligence process.
What if a client does not have a TFN? Ask them to enter 000 000 000. This is the ATO's standard code for a TFN that has not been quoted, and the form accepts it, even when the TFN question is mandatory. It suits clients who do not have a TFN, such as some non-residents. Other placeholders, such as 999 999 999, fail the checksum and will not be accepted. Make a note on the client's record that no TFN was provided.