What type of tax requires the same fraction of income from all taxpayers?

A proportional tax, also known as a flat tax, is designed to impose the same percentage of income on all taxpayers, regardless of their income level. This means that each individual pays the same fraction of their income, which results in an equal distribution of the tax rate across different income brackets. For example, if the proportional tax rate is set at 10%, every taxpayer, regardless of whether they earn $30,000 or $300,000 per year, would pay 10% of their respective income.

In contrast, a progressive tax system is structured so that higher income earners pay a larger percentage of their income in taxes compared to lower income earners. Conversely, a regressive tax system takes a larger percentage of income from lower earners than from higher earners, often placing a heavier tax burden on those with less ability to pay. A luxury tax is typically applied to goods that are considered non-essential or luxury items and is not centered around income levels. Each of these other tax types has distinct characteristics that differentiate them from a proportional tax, which is unique in its equal treatment of all taxpayers in terms of the tax rate applied.