The ATO produce tax calculators to help you work out your tax refund or debt estimate for previous years. You can use these to estimate your tax payable and also calculate your:
Medicare levy
Medicare levy surcharge
Higher Education Loan Program (HELP)/Trade Support Loan (TSL) repayment
Student Financial Supplement Scheme (SFSS) repayment
any tax offsets that may apply.
Check out the ATO Complex Tax Calculator website.