In economics, a negative income tax (abbreviated NIT) is a progressive income tax system where people earning below a certain amount receive supplemental pay from the government instead of paying taxes to the government. Such a system has been discussed by economists but never fully implemented. It was developed by British politician Juliet Rhys-Williams in the 1940s^{[citation needed]} and later United States economist Milton Friedman combined NIT with his flat tax proposals.

Negative income taxes can implement a basic income or supplement a guaranteed minimum income system.

In a negative income tax system, people earning a certain income level would owe no taxes; those earning more than that would pay a proportion of their income above that level; and those below that level would receive a payment of a proportion of their shortfall, which is the amount their income falls below that level.

A negative income tax is intended to create a single system that would not only pay for government, but would also fulfill the social goal of making sure that there was a minimum level of income for all. It is theorized that, with an NIT, the need for minimum wage, food stamps, welfare, social security programs and other government assistance programs could be eliminated, thus reducing the administrative effort and cost to a fraction of what it is under the current system, as well as eliminating the perverse incentives created by these overlapping aid programs, e.g. when a minimum wage worker who earns a little more nets out with less income because he is newly ineligible for aid. The worker is stuck in a welfare trap and has no incentive to seek higher wages.

An income tax is a tax levied on the income of individuals or businesses (corporations or other legal entities). Various income tax systems exist, with varying degrees of tax incidence. Income taxation can be progressive, proportional, or regressive. When the tax is levied on the income of companies, it is often called a corporate tax, corporate income tax, or profit tax. Individual income taxes often tax the total income of the individual (with some deductions permitted), while corporate income taxes often tax net income (the difference between gross receipts, expenses, and additional write-offs). Various systems define income differently, and often allow notional reductions of income (such as a reduction based on number of children supported).

The "tax net" refers to the types of payment that are taxed, which included personal earnings (wages), capital gains, and business income. The rates for different types of income may vary and some may not be taxed at all. Capital gains may be taxed when realized (e.g. when shares are sold) or when incurred (e.g. when shares appreciate in value). Business income may only be taxed if it is significant or based on the manner in which it is paid. Some types of income, such as interest on bank savings, may be considered as personal earnings (similar to wages) or as a realized property gain (similar to selling shares). In some tax systems, personal earnings may be strictly defined where labor, skill, or investment is required (e.g. wages); in others, they may be defined broadly to include windfalls (e.g. gambling wins).

Milton Friedman (July 31, 1912 – November 16, 2006) was an American economist, statistician, and author who taught at the University of Chicago for more than three decades. He was a recipient of the Nobel Memorial Prize in Economic Sciences, and is known for his research on consumption analysis, monetary history and theory, and the complexity of stabilization policy. As a leader of the Chicago school of economics, he influenced the research agenda of the economics profession. A survey of economists ranked Friedman as the second most popular economist of the twentieth century behind John Maynard Keynes, and The Economist described him as "the most influential economist of the second half of the 20th century…possibly of all of it."

Friedman's challenges to what he later called "naive Keynesian" (as opposed to New Keynesian) theory began with his 1950s reinterpretation of the consumption function, and he became the main advocate opposing activist Keynesian government policies. In the late 1960s he described his own approach (along with all of mainstream economics) as using "Keynesian language and apparatus" yet rejecting its "initial" conclusions. During the 1960s he promoted an alternative macroeconomic policy known as "monetarism". He theorized there existed a "natural" rate of unemployment, and argued that governments could increase employment above this rate (e.g., by increasing aggregate demand) only at the risk of causing inflation to accelerate. He argued that the Phillips curve was not stable and predicted what would come to be known as stagflation. Friedman argued that, given the existence of the Federal Reserve, a constant small expansion of the money supply was the only wise policy.