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 of certain types of business expenses. Individuals are also allowed credits related to education expenses, retirement savings, child care expenses, some health care premiums, and a credit for each child. Each of the credits is subject to specific rules and limitations. Some credits are treated as refundable payments. Alternative Minimum Tax: All taxpayers are also subject to the Alternative Minimum Tax if their income exceeds certain exclusion amounts. This tax applies only if it exceeds regular income tax, and is reduced by some credits. Additional Medicare Tax: High-income earners may also have to pay an additional 0.9% tax on wages,