Rates are set by fiscal year, effective October 1 each year. Find current rates in the continental United States ("CONUS Rates").
Estimated taxes may be paid by individuals who either:
Unlike employees, who have employment taxes withheld from their gross pay by their employer, sole proprietors and general partners are not classified as employees of their business; they are self-employed and therefore, are not subject to employment tax withholding.
A self-employed person generally is required to pay estimated taxes to cover federal income taxes and self-employment taxes (which are social security and Medicare taxes)
Estimated tax requirements are different for farmers and fisherman. See Publication 505, Tax Withholding and Estimated Tax, for more information.
C corporations also pay estimated taxes.