If the rate of tax decreases with the increase in tax base, then the tax is said to be

A tax is classified as a regressive tax when the average rate of taxation decreases as the tax base (such as income or wealth) increases, placing a heavier relative burden on lower-income taxpayers. By contrast, a progressive tax has a rate that rises as the tax base increases, a proportional tax levies a constant percentage regardless of the size of the tax base, and a degressive tax rises at a diminishing rate up to a certain threshold before becoming proportional.