Income tax is levied on taxable income, which is calculated as [assessable income] less [any allowable deductions]. Deductions include wages, cost of stock, rent, bad debts, and previous year losses.
You can use the tax tables to determine how much you are taxed.
A company is a distinct legal entity with its own income tax liability so a company tax return must be completed for each company. A company's income tax is calculated as a percentage of the taxable income the company earned during the financial year. The company tax rate is 30%.
From 1 July 2015 this had been reduced to 28.5% for all small businesses (with aggregated turnover of less than $2 million).
A partnership running a business must complete a partnership tax return to show all income earned and deductions claimed for expenses during the course of the business and how the profit or loss was shared between the partners. Each partner pays tax on their share of the partnership's income so they must include their individual share of the net partnership profit or loss in their personal tax return.
Sole traders are not required to complete a separate return for their business. They use their personal income tax return to report their business income and deductions.