The IRS has announced that interest rates for the calendar quarter beginning October 1, 2010, will remain the same. The interest rates will be 4% for overpayments (3% in the case of a corporation) and underpayments, 6% for large corporate underpayments and 1.5% for the portion of a corporate overpayment exceeding $10,000. The interest rates are computed by using the federal short-term rate based on daily compounding determined during July 2010. The rate of interest is determined on a quarterly basis. (Rev. Rul. 2010-21, IRB. 2010-39, September 27, 2010; IR-2010-90, August 19, 2010.)
The states of Alabama and South Carolina follow the federal underpayment rate. Pennsylvania follows the federal rate in effect as of January 1 of the calendar year, without regard to quarterly changes. Illinois follows the federal underpayment rate as of January 1 and July 1 of the calendar year. Additionally, Virginia's interest rate on tax underpayments is the federal interest rate plus 2%, while Arizona's is the federal short-term rate plus three percentage points.