Income tax return for taxation also vary, making comparisons all the more difficult. Countries that tax income generally use one of two systems: territorial or residential. In the territorial system, only local income – income from a source inside the country – is taxed. In the residential system, residents of the country are taxed on their worldwide (local and foreign) income, while nonresidents are taxed only on their local income. In addition, a very small number of countries, notably the United States, also tax their nonresident citizens on worldwide income. Countries with a residential system of taxation usually allow deductions or credits
Income tax in the United States made frequently to change tax laws, often with the backing of specific interest groups. Organizations making such proposals include Citizens for Tax Justice, Americans for Tax Reform, Americans for Tax Fairness, Citizens for an Alternative Tax System, Americans For Fair Taxation, and FreedomWorks. Various proposals have been put forth for tax simplification in Congress including the "Fair Tax Act" and various Flat tax plans. Proponents of a consumption tax argue that the income tax system creates perverse incentives by encouraging taxpayers to spend rather than save: a taxpayer is only taxed once on income spent immediately, while any interest earned