According to their newest press release, the IRS is announced earlier today that interest  rates for the first quarter of 2009 (beginning January 1, 2009) will  drop by one percentage.
 The new rates will be: 
 - Five (5) percent for overpayments    [four (4) percent in the case of a corporation];
- Five (5) percent for underpayments;
- Seven (7) percent for large    corporate underpayments; and
- Two and one-half (2.5) percent    for the portion of a corporate overpayment exceeding $10,000.
“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.”