Revenue Ruling 2021-21  provides various prescribed rates for federal income tax purposes including the applicable federal interest rates, the adjusted applicable federal interest rates, the adjusted federal long-term rate, and the adjusted federal long-term tax-exempt rate. These rates are determined as prescribed by § 1274.  

The rates are published monthly for purposes of sections 42, 382, 412, 642, 1288, 1274, 7520, 7872, and various other sections of the Internal Revenue Code.