In Australia, a Tax File Number (TFN) declaration form is a document provided by the Australian Taxation Office (ATO) that individuals use to declare their tax file number to their employer. A TFN is a unique identifier issued by the ATO to individuals and organizations to help manage tax and other government services.

When starting a new job or changing jobs, employees are required to provide their TFN to their employer. The TFN declaration form includes personal details such as name, address, date of birth, and the TFN itself. This information is used by the employer to withhold the correct amount of tax from the employee's pay according to their tax obligations.

By providing their TFN, individuals authorize their employer to withhold tax from their pay at the appropriate rate. Without a TFN declaration, the employer may be required to withhold tax at the highest marginal tax rate, which could result in the employee paying more tax than necessary.

The TFN declaration form also includes options for additional tax withholding, such as the Medicare Levy and the Temporary Budget Repair Levy (if applicable). Employees can choose to claim certain tax offsets or exemptions on this form as well. The TFN declaration must be keep on file for a minimum of 5 years.