Proportional tax
（重定向自Proportional tax rate）
A proportional tax is a tax imposed so that the tax rate is fixed, with no change as the taxable base amount increases or decreases. The amount of the tax is in proportion to the amount subject to taxation. "Proportional" describes a distribution effect on income or expenditure, referring to the way the rate remains consistent (does not progress from "low to high" or "high to low" as income or consumption changes), where the marginal tax rate is equal to the average tax rate.