What characteristic defines a proportional tax?

A proportional tax is characterized by a constant tax rate that applies equally to all income levels. This means that taxpayers pay the same percentage of their income in taxes, regardless of how much they earn. For instance, if the tax rate is set at 10%, both a person earning $30,000 and another earning $300,000 will pay 10% of their respective incomes in taxes. This system is designed to be fair in the sense that everyone contributes the same proportion of their income, promoting a sense of equality in taxation.

Other tax structures vary with income levels. A tax rate that changes based on income, where higher incomes are taxed at higher rates, would be considered a progressive tax. This approach generally aims to alleviate the tax burden on lower-income earners. In contrast, a regressive tax disproportionately affects lower-income individuals, as it takes a larger percentage of their income compared to higher earners, illustrating how a proportional system differs in its steady application across income levels. The last option would describe a progressive system where only those in higher income brackets are taxed at higher rates.