A corporate tax is a levy which the government imposes on the income of a company. The money collected from corporate taxes is used as the source of revenue for a country. The operating earnings of a company are determined by deducting costs from the cost of the product sold (COGS) and income depreciation. Businesses Taxed as Corporations The rules you must use to determine whether a business is taxed as a corporation changed for businesses formed after 1996. The business was formed before 1997. A business formed before 1997 and taxed as a corporation under the old rules will generally continue to be taxed as a corporation.