What is the difference between a progressive tax, a proportional tax, and a regressive tax?

A progressive tax is a tax where the rate increases as income increases, ensuring higher-income individuals pay a higher percentage of their income in taxes. An example is the US federal income tax system. A proportional tax, or flat tax, has a constant tax rate regardless of income levels, ensuring equal treatment of all taxpayers. An example is a flat 5% sales tax on all goods and services. A regressive tax is a tax where the rate decreases as income increases, burdening lower-income individuals more. An example is a sales tax on essential goods like food and clothing, as lower-income individuals spend a larger proportion of their income on these items. In summary, the differences lie in their rates' changes with income: progressive-tax rates increase, proportional-tax rates remain constant, and regressive-tax rates decrease as income increases.