In Australia, ticking “Yes” to the tax-free threshold question on your Tax File Number (TFN) Declaration tells your employer not to withhold tax on the first $18,200 of your annual earnings.

If you work two jobs at the same time and accidentally claim the threshold on both, each employer will assume they are your only source of income. This means both payroll systems will process your weekly or fortnightly pay cycles without withholding enough tax. While it gives you a higher take-home pay during the year, it creates an artificial deficit that the Australian Taxation Office (ATO) will square up when you lodge your tax return.

1. The Imminent Consequence: A Surprise Tax Bill

The ATO does not view your jobs as isolated accounts. When you lodge your end-of-year tax return, Single Touch Payroll (STP Phase 2) data automatically aggregates your total global earnings.

• The Math Deficit: Instead of protecting just the single legal threshold of $18,200, your dual claims mean you have effectively gone untaxed on up to $36,400 of combined income throughout the year.
• The Debt: Because the correct progressive tax rates were not applied progressively on your second income stream, you will owe the ATO a lump-sum tax bill to cover the under-withheld amount.

The Exception: If your combined annual income across both jobs combined is guaranteed to be less than $18,200, claiming the threshold on both is completely fine and will not trigger a debt, as your total income remains entirely tax-free.

2. How to Fix the Mistake Immediately

You do not need to wait until tax time to correct this error. Adjusting your settings mid-year stops the tax debt from growing larger.

Method A: The Digital Update via myGov (Fastest)

1. Log into your myGov account and select ATO Online Services.
2. Navigate to the Employment menu and select New Employment.
3. Choose the employer where you earn the least amount of money (your secondary job).
4. Submit a fresh Withholding Declaration online, ensuring you select “No” to the question: “Do you want to claim the tax-free threshold from this payer?”

Method B: The Paper Form

Request a physical Withholding Declaration form (NAT 3093) from your secondary employer’s payroll or HR department. Fill out your details, check “No” to the threshold option, and return it to them. They are legally required to update your payroll profile for the very next pay cycle.

Dual Claim Financial Impact Case Study

3. What If You Face a Debt at Tax Time?

If you discover the mistake late in the financial year and your calculation reveals a looming debt, do not panic or avoid lodging your tax return.

• No Penalty for Accidental Claims: The ATO will not fine or penalize you for accidentally ticking the wrong box on your TFN declaration. They simply require the missing tax principal to be paid.
• Interest-Free Payment Plans: If your resulting tax assessment bill is too large to clear in a single payment, you can easily set up a automated, interest-free or low-interest payment plan directly inside your myGov portal to pay down the debt in manageable weekly or fortnightly installments.