be constant (flat) by income level. Many systems allow individuals certain personal allowances and other non-business reductions to taxable income, although business deductions tend to be favored over personal deductions. Tax-collection agencies often collect personal income tax on a pay-as-you-earn basis, with corrections made after the end of the tax year. These corrections take one of two forms: payments to the government, from taxpayers who have not paid enough during the tax year tax refunds from the government to those who have overpaid Income-tax systems often make deductions available that reduce the total tax liability by reducing total taxable income. They may allow losses from one type of income to count against another - for example, a loss on the stock market may be deducted against taxes paid on wages. Other tax systems may isolate the loss, such that business losses can only be deducted against business income tax by carrying forward the loss to later tax years. Negative income tax In economics, a negative income tax (abbreviated NIT) is a progressive income tax system where people earning below a certain amount receive supplemental payment from the government instead of paying taxes to the government. Capital gains Most jurisdictions imposing an income tax treat capital gains as part of income subject to tax. Capital gain is generally a gain on sale of capital assets—that is, those assets not held for sale in the ordinary course of business. Capital assets include personal assets in many jurisdictions. Some jurisdictions provide preferential rates of tax or only partial taxation for capital gains. Some jurisdictions impose different rates or levels of capital-gains taxation based on the length of time the asset was held. Because tax rates are often much lower for capital gains than for ordinary income, there is widespread controversy and dispute about the proper definition of capital. Corporate Corporate tax refers to income tax, capital tax, net-worth tax, or other taxes imposed on corporations. Rates of tax and the taxable base for corporations may differ from those for individuals or for other taxable persons. Social-security contributions Many countries provide publicly funded retirement or healthcare systems. In connection with these systems, the country typically requires employers and/or employees to make compulsory payments. These payments are often computed by reference to wages or earnings from self-employment. Tax rates are generally fixed, but a different rate may be imposed on employers than on employees. Some