In Australia, the tax free threshold is around $18,200 per year. When you start a new job, you will be asked for fill in a tax declaration and one of the questions you will be asked is:
“Do you want to claim the tax free threshold from this employer?”

if second payer does not withhold a higher rate of tax you may owe money If you say yes to this question, this means that the employer will not calculate tax on the first $18,200 that you earn. However, if you have a second job, you should answer “No” to this question.
If you answer “Yes”, the second employer will also not deduct any tax from the first $18,200 you earn.

This means when it comes time to prepare your income tax return for that financial year, you will find that you have not paid enough tax on your income, and will be hit with a debt to the Australian Tax Office (ATO).

Do you have a second job? See the page which explains how lodging a tax return online works. Then follow the steps to lodge your tax online now.

How Much Tax Will You Pay For A Second Job

Watch this video for some information with David Koche on how the ATO operate in Australia and some tips and tricks to help you

withholding variation application e-variation
Visit our How It Works page and follow the steps to lodge your tax online now.

This Audio File Explains how The ATO Apply The Tax Rate To Income From A Second Job