A proportional tax rate structure is a tax where the tax rate remains at the same rate regardless of the tax base.

A proportional tax rate structure is also known as a flat-rate tax. It means that the tax rate remains the same for all taxpayers, regardless of their income level or the size of their tax base. This is different from a progressive tax where the tax rate increases as the tax base increases, and a regressive tax where the tax rate decreases as the tax base increases.