A flat tax (short for flat-rate tax) is a tax with a single rate on the taxable amount, after accounting for any deductions or exemptions from the tax base. It is not necessarily a fully proportional tax. Implementations are often progressive due to exemptions, or regressive in case of a maximum taxable amount. There are various tax systems that are labeled "flat tax" even though they are significantly different. The defining characteristic is the existence of only one tax rate other than zero, as opposed to multiple non-zero rates that vary depending on the amount subject to taxation.
A flat tax system is usually discussed in the context of an income tax, where progressivity is common, but it may also apply to taxes on consumption, property or transfers.
Major categories Flat tax proposals differ in how the subject of the tax is defined.
True flat-rate income tax A true flat-rate tax is a system of taxation where one tax rate is applied to all personal income with no deductions.
Marginal flat tax Where deductions are allowed, a 'flat tax' is a progressive tax with the special characteristic that, above the maximum deduction, the marginal rate on all further income is constant. Such a tax is said to be marginally flat above that point. The difference between a true flat tax and a marginally flat tax can be reconciled by recognizing that the latter simply excludes certain types of income from being defined as taxable income; hence, both kinds of tax are flat on taxable income.
Flat tax with limited deductions Modified flat taxes have been proposed which would allow deductions for a very few items, while still eliminating the vast majority of existing deductions. Charitable deductions and home mortgage interest are the most discussed examples of deductions that would be retained, as these deductions are popular with voters and are often used. Another common theme is a single, large, fixed deduction. This large fixed deduction would compensate for the elimination of various existing deductions and would simplify taxes, having the side-effect that many (mostly low income) households will not have to file tax returns.
Hall–Rabushka flat tax
Designed by economists at the Hoover Institution, Hall–Rabushka is a flat tax on consumption.The Flat Tax, Robert E. Hall and Alvin Rabushka, Hoover Institution, 2 April 2007. Principally, Hall–Rabushka accomplishes a consumption tax effect by taxing income and then excluding investment. Robert Hall and Alvin Rabushka have consulted extensively in designing the flat tax systems in Eastern Europe.
Negative income tax
The negative income tax (NIT), which Milton Friedman proposed in his 1962 book Capitalism and Freedom, is a type of flat tax. The basic idea is the same as a flat tax with personal deductions, except that when deductions exceed income, the taxable income is allowed to become negative rather than being set to zero. The flat tax rate is then applied to the resulting "negative income," resulting in a "negative income tax" that the government would owe to the household—unlike the usual "positive" income tax, which the household owes the government.
For example, let the flat rate be 20%, and let the deductions be $20,000 per adult and $7,000 per dependent. Under such a system, a family of four making $54,000 a year would owe no tax. A family of four making $74,000 a year would owe tax amounting to 0.20 × (74,000 − 54,000) = $4,000, as would be the case under a flat tax system with deductions. Families of four earning less than $54,000 per year, however, would experience a "negative" amount of tax (that is, the family would receive money from the government instead of paying to the government). For example, if the family earned $34,000 a year, it would receive a check for $4,000. The NIT is intended to replace not just the USA's income tax, but also many benefits low income American households receive, such as food stamps and Medicaid. The NIT is designed to avoid the welfare trap—effective high marginal tax rates arising from the rules reducing benefits as market income rises. An objection to the NIT is that it is welfare without a work requirement. Those who would owe negative tax would be receiving a form of welfare without having to make an effort to obtain employment. Another objection is that the NIT subsidizes industries employing low-cost labor, but this objection can also be made against current systems of benefits for the working poor.
Capped flat tax A capped flat tax is one in which income is taxed at a flat rate until a specified cap amount is reached. For example, the United States Federal Insurance Contributions Act tax is 6.2% of gross compensation up to a limit (in 2025, up to $176,100 of earnings, for a maximum tax of $10,918.20).Contribution and Benefit Base, United States Social Security Administration. This cap has the effect of turning a nominally flat tax into a regressive tax.Are Social Security taxes regressive?, The Economist, 14 April 2009.
Requirements for a fully defined schema In devising a flat tax system, several recurring issues must be enumerated, principally with deductions and the identification of when money is earned.
Defining when income occurs Since a central tenet of the flat tax is to minimize the compartmentalization of incomes into myriad special or sheltered cases, a vexing problem is deciding when income occurs. This is demonstrated by the taxation of interest income and stock dividends. The shareholders own the company and so the company's profits belong to them. If a company is taxed on its profits, then the funds paid out as dividends have already been taxed. It's a debatable question if they should subsequently be treated as income to the shareholders and thus subject to further tax. A similar issue arises in deciding if interest paid on loans should be deductible from the taxable income since that interest is in-turn taxed as income to the loan provider. There is no universally agreed answer to what is fair. For example, in the United States, dividends are not deductible but mortgage interest is deductible.Publication 936 (2021), Home Mortgage Interest Deduction, 5 January 2022. Thus a Flat Tax proposal is not fully defined until it differentiates new untaxed income from a pass-through of already taxed income.
Policy administration Taxes, in addition to providing revenue, can be potent instruments of policy. For example, it is common for governments to encourage social policy such as home insulation or low income housing with tax credits rather than constituting a ministry to implement these policies.Federal Income Tax Credits and Other Incentives for Energy Efficiency , Energy Star. In a flat tax system with limited deductions such policy administration, mechanisms are curtailed. In addition to social policy, flat taxes can remove tools for adjusting economic policy as well. For example, in the United States, short-term capital gains are taxed at a higher rate than long-term gains as means to promote long-term investment horizons and damp speculative fluctuation. Thus, if one assumes that government should be active in policy decisions such as this, then claims that flat taxes are cheaper/simpler to administer than others are incomplete until they factor in costs for alternative policy administration.
Minimizing deductions In general, the question of how to eliminate deductions is fundamental to the flat tax design; deductions dramatically affect the effective "flatness" in the tax rate. Perhaps the single biggest necessary deduction is for business expenses. If businesses were not allowed to deduct expenses, businesses with a profit margin below the flat tax rate could never earn any money since the tax on revenues would always exceed the earnings. For example, grocery stores typically earn pennies on every dollar of revenue; they could not pay a tax rate of 25% on revenues unless their markup exceeded 25%. Thus, corporations must be able to deduct operating expenses even if individuals cannot. A practical dilemma arises as to identifying what is an expense for a business. For example, if a peanut butter producer purchases a jar manufacturer, is that an expense (since the producer has to purchase jars somehow) or a sheltering of income through investment? Flat tax systems can differ greatly in how they accommodate such gray areas. For example, the "9-9-9" flat tax proposal would allow businesses to deduct purchases but not labor costs, which effectively taxes labor-intensive industrial revenue at a higher rate.Herman Cain's 9-9-9 Tax Plan, Edward D. Kleinbard, Social Science Research Network, 24 October 2011. How deductions are implemented will dramatically change the effective total tax, and thus the flatness of the tax. Thus, a flat tax proposal is not fully defined unless the proposal includes a differentiation between deductible and non-deductible expenses.
Tax effects
Diminishing marginal utility Flat tax benefits higher income brackets progressively due to decline in marginal value.The Consumer: Marginal Value, Marginal Utility, and Consumer Surplus, Price Theory: An Intermediate Text, David D. Friedman, 1990. If a flat tax system has a large exemption, it is effectively a progressive tax. As a result, the term "flat tax" is actually a shorthand for the more proper marginally flat tax.
Administration and enforcement One type of flat tax would be imposed on all income once: at the source of the income. Hall and Rabushka proposed an amendment to the U.S. Internal Revenue Code that would implement the variant of the flat tax they advocate. This amendment, only a few pages long, would replace hundreds of pages of statutory language (although most statutory language in taxation statutes is not directed at specifying graduated tax rates).
As it now stands, the U.S. Internal Revenue Code is over several million words long, and contains many loopholes, deductions, and exemptions which, advocates of flat taxes claim, render the collection of taxes and the enforcement of tax law complicated and inefficient.
It is further argued that current tax law slows economic growth by distorting economic incentives, and by allowing, even encouraging, tax avoidance. With a flat tax, there are fewer incentives than in the current system to create tax shelters, and to engage in other forms of tax avoidance.
Flat tax critics contend that a flat tax system could be created with many loopholes, or a progressive tax system without loopholes, and that a progressive tax system could be as simple, or simpler, than a flat tax system. A simple progressive tax would also discourage tax avoidance.
Under a pure flat tax without deductions, every tax period a company would make a single payment to the government covering the taxes on the employees and the taxes on the company profit. For example, suppose that in a given year, a company called ACME earns a profit of 3 million, spends 2 million in wages, and spends 1 million on other expenses that under the tax law is taxable income to recipients, such as the receipt of stock options, bonuses, and certain executive privileges. Given a flat rate of 15%, ACME would then owe the U.S. Internal Revenue Service (IRS) (3M + 2M + 1M) × 0.15 = 900,000. This payment would, in one fell swoop, settle the tax liabilities of ACME's employees as well as the corporate taxes owed by ACME. Most employees throughout the economy would never need to interact with the IRS, as all tax owed on wages, interest, dividends, royalties, etc. would be withheld at the source. The main exceptions would be employees with incomes from personal ventures. The Economist claims that such a system would reduce the number of entities required to file returns from about 130 million individuals, households, and businesses, as at present, to a mere 8 million businesses and self-employed.