Proportional, progressive, and regressive taxes

Taxes can be distinguished by the effect they have on the distribution of income and wealth. A proportional tax is one that imposes the same relative burden on all taxpayers—i.e., where tax liability and income grow in equal proportion. A progressive tax is characterized by a more than proportional rise in the tax liability relative to the increase in income, and a regressive tax is characterized by a less than proportional rise in the relative burden. Thus, progressive taxes are seen as reducing inequalities in income distribution, whereas regressive taxes can have the effect of increasing these inequalities.

The taxes that are generally considered progressive include individual income taxes and estate taxes. Income taxes that are nominally progressive, however, may become less so in the upper-income categories—especially if a taxpayer is allowed to reduce his tax base by declaring deductions or by excluding certain income components from his taxable income. Proportional tax rates that are applied to lower-income categories will also be more progressive if personal exemptions are declared.

Income measured over the course of a given year does not necessarily provide the best measure of taxpaying ability. For example, transitory increases in income may be saved, and during temporary declines in income a taxpayer may choose to finance consumption by reducing savings. Thus, if taxation is compared with “permanent income,” it will be less regressive (or more progressive) than if it is compared with annual income.

Sales taxes and excises (except those on luxuries) tend to be regressive, because the share of personal income consumed or spent on a specific good declines as the level of personal income rises. Poll taxes (also known as head taxes), levied as a fixed amount per capita, obviously are regressive.

It is difficult to classify corporate income taxes and taxes on business as progressive, regressive, or proportionate, because of uncertainty about the ability of businesses to shift their tax expenses (see below Shifting and incidence). This difficulty of determining who bears the tax burden depends crucially on whether a national or a subnational (that is, provincial or state) tax is being considered.

In considering the economic effects of taxation, it is important to distinguish between several concepts of tax rates. The statutory rates are those specified in the law; commonly these are marginal rates, but sometimes they are average rates. Marginal income tax rates indicate the fraction of incremental income that is taken by taxation when income rises by one dollar. Thus, if tax liability rises by 45 cents when income rises by one dollar, the marginal tax rate is 45 percent. Income tax statutes commonly contain graduated marginal rates—i.e., rates that rise as income rises. Careful analysis of marginal tax rates must consider provisions other than the formal statutory rate structure. If, for example, a particular tax credit (reduction in tax) falls by 20 cents for each one-dollar rise in income, the marginal rate is 20 percentage points higher than indicated by the statutory rates. Since marginal rates indicate how after-tax income changes in response to changes in before-tax income, they are the relevant ones for appraising incentive effects of taxation. It is even more difficult to know the marginal effective tax rate applied to income from business and capital, since it may depend on such considerations as the structure of depreciation allowances, the deductibility of interest, and the provisions for inflation adjustment. A basic economic theorem holds that the marginal effective tax rate in income from capital is zero under a consumption-based tax.

Average income tax rates indicate the fraction of total income that is paid in taxation. The pattern of average rates is the one that is relevant for appraising the distributional equity of taxation. Under a progressive income tax the average income tax rate rises with income. Average income tax rates commonly rise with income, both because personal allowances are provided for the taxpayer and dependents and because marginal tax rates are graduated; on the other hand, preferential treatment of income received predominantly by high-income households may swamp these effects, producing regressivity, as indicated by average tax rates that fall as income rises.