IR-2021-173, August 25, 2021 WASHINGTON — The Internal Revenue Service today announced that interest rates will remain the same for the calendar quarter beginning October 1, 2021. The rates will be: 3% for overpayments (2% in the case of a corporation); 0.5 % for the portion of a corporate overpayment exceeding $10,000; 3% percent for underpayments; and 5% percent for large corporate underpayments. Under the Internal Revenue Code, the rate of interest is determined on a quarterly basis. For taxpayers other than corporations, the overpayment and underpayment rate is the federal short-term rate plus 3 percentage points. Generally, in the case of a corporation, the underpayment rate is the federal short-term rate plus 3 percentage points and the overpayment rate is the federal short-term rate plus 2 percentage points. The rate for large corporate underpayments is the federal short-term rate plus 5 percentage points. The rate on the portion of a corporate overpayment of tax exceeding $10,000 for a taxable period is the federal short-term rate plus one-half (0.5) of a percentage point. The interest rates announced today are computed from the federal short-term rate determined during July 2021 to take effect August 1, 2021, based on daily compounding. Revenue Ruling 2021-17PDF, announcing the rates of interest, will appear in Internal Revenue Bulletin 2021-37, dated September 13, 2021.