The corporate income tax is a levy that is imposed on the net profits of corporations, computed as the excess of receipts over allowable costs.

The separate taxation of the incomes of corporations and their shareholders follows the legal principle that corporations and shareholders are distinct entities. Some scholars argue that it also accords with economic reality, particularly for large corporations with many shareholders who do not participate actively in controlling the enterprise. They consider a corporation income tax justified as a charge for the privilege of doing business in the corporate form, as a means of covering the costs of public services that especially benefit business, and as a way of capturing part of the profits of large enterprises.

Other scholars maintain that corporations act on behalf of shareholders and should be taxed like a large partnership or, alternatively, only to the extent that their profits are not reached by the individual income tax. Most economists concede that a tax may have to be assessed on corporations to prevent shareholders from escaping current taxation on undistributed profits and, as their shares appreciate in value, converting this income into capital gains, which in many countries either are taxed at lower rates than ordinary income or are free of income tax. (See capital gains tax.) A corporation income tax also enables a country, province, or state to tax the profits earned within its borders by corporations whose shareholders reside elsewhere.

Corporate income taxes are mainly flat-rate levies, rather than extensively graduated taxes (which means that rates rise according to income—as in the typical individual income tax). An acceptable schedule of progressive rates could hardly be devised for corporations, because they differ greatly in scale of operations and numbers of shareholders. (See progressive tax.) Moreover, the shareholders themselves may have either high incomes or (as is the case with corporate pension funds) low incomes.

A number of industrialized countries have corporate income tax rates on the order of 50 percent, sometimes with reduced rates for small corporations. Where the latter feature exists, safeguards may be instituted to prevent its abuse by enterprises that split into nominally independent corporations without giving up unified control. More significant are corporate mergers or acquisitions motivated by the possibility of saving taxes through offsetting the losses of some against the profits of others.

Corporate taxes may be graduated according to the rate of return on invested capital rather than the absolute size of profits. This is accomplished by an excess-profits tax on profits above a certain “normal” rate of return, sometimes further graduated according to the degree to which actual profits exceed the exempt level. The excess-profits tax has been used widely during wars and other national emergencies and to a much lesser extent under other conditions. There are serious difficulties involved in determining accurately the value of invested capital and in selecting an appropriate normal rate of return.

Sharp differences of opinion exist concerning the economic effects of the corporate income tax, partly because it is difficult to determine who actually bears it. The traditional conclusion of economic theory is that the tax is not reflected in prices in the short run and hence must be paid out of profits. If firms try to maximize their profits, the tax will give them no reason to change their prices. The price and output that yield maximum profits before tax will yield maximum profits after tax. Although the tax must be covered by sales receipts, it is not a cost of production in the same sense as, for example, wages but a share of profits that can be computed only after gross receipts and production costs are known. This reasoning applies equally to competitive and to less-competitive or wholly monopolized industries. Certain qualifications have always been made, but they are fairly minor in nature. More important, the theory relates only to the determination of prices and output given the existing stock of capital. (The technical definition of short run in economics is a period of time over which the capital stock does not change.) The theory does not predict what the long-run effects of the tax will be, although it indicates that they will mirror those of a tax on profit recipients rather than on consumers.

This view of the incidence of the corporate income tax has been increasingly challenged. Its opponents argue that in many industries prices are decisively influenced by the actions of a few leading firms, which have as their objective not maximum profits in the short run but a target rate of return over a period of years. When the rate of corporate income tax is increased, they say, the leading firms will raise their selling prices in order to maintain the target return, and other firms will follow. According to this hypothesis, prices are not competitively determined but are generally at levels lower than those that would yield maximum profits in the short run. Another qualification of the traditional view is that labour unions may share the burden of the tax through lower wage settlements.

The debate among economists and businessmen over the question has not been resolved by empirical research. Some studies in the United States, Canada, and Germany indicate that the corporate income tax is largely shifted to consumers through short-run price rises, while other studies support the opposite conclusion.

If the tax is not shifted to consumers through price increases, it will tend to reduce the return on corporate-equity capital. (Because interest payments are nearly always deductible in determining taxable profits, the return on borrowed capital is not subject to the corporation tax.) The returns on capital in unincorporated enterprises and on bonds and mortgages will tend to fall over time as investors try to avoid the corporate tax by shifting to untaxed areas. In this way the corporation income tax may actually burden all capital, rather than only that invested in the corporate sector. A general reduction in rates of return may curtail investment by cutting the reward for success and by reducing the quantity of resources available in the form of retained corporate profits and personal savings. This will tend to reduce the rate of growth of national product. Ultimately, however, the effect may not be dramatic. Capital investment is only one factor influencing growth rates, and some analyses indicate that it is less important than other phenomena, such as technological innovation and education, that influence the growth rate.

If the corporate income tax reduces either the return on corporate-equity capital or the returns on all capital, it will be broadly progressive in the aggregate; that is, it will reduce disposable income proportionately more for high-income persons than for low-income persons. This is because the fraction of total income represented by returns from ownership of corporate stock and other capital assets rises with income. This effect holds, however, only in the aggregate, because some low-income people, including many retirees, depend heavily on investment income and on the capital that has accumulated in pension funds.

On the other hand, when the corporate income tax is passed along to consumers through higher prices, it will—like a sales tax—act as a regressive tax, reducing disposable income proportionately more for people with low incomes than for those with high incomes. A corporation tax that has been shifted to consumers will not be especially harmful to investment, but it may have an adverse effect on resource allocation and a company’s competitive position in foreign markets.

Moreover, the effects of taxes imposed by a subnational government will differ from the effects of taxes imposed by a national government. A state tax, for example, is more likely to be borne by consumers residing in the state, by employees who work in the state, or by those who own land in the state.