A proportional tax is a tax that is applied at a fixed rate, regardless of the amount of income. In other words, the rate of a proportional tax does not change with income. For example, if the tax rate is 10%, then a person who earns $100 will pay $10 in tax, and a person who earns $1000 will pay $100 in tax. The amount of tax paid will be proportional to the income earned, but the rate at which the tax is applied will remain the same.