Revenue Ruling 2021-05 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.

Notice 2021-16 provides guidance on the corporate bond monthly yield curve, the corresponding spot segment rates used under § 417(e)(3), and the 24-month average segment rates under § 430(h)(2) of the Internal Revenue Code.  In addition, this notice provides guidance as to the interest rate on 30-year Treasury securities under § 417(e)(3)(A)(ii)(II) as in effect for plan years beginning before 2008 and the 30-year Treasury weighted average rate under § 431(c)(6)(E)(ii)(I), as reflected by the application of § 430(h)(2)(C)(iv). 

Revenue Ruling 2021-05 and Notice 2021-16 will be in IRB:  2021-10, dated March 8, 2021.