The Internal Revenue Service has announced in Revenue Ruling 2008-54 that interest rates for the calendar quarter beginning January 1, 2009 will drop by one percentage point. 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.

These new interest rates are computed from the federal short-term rate during October 2008 to take effect Nov. 1, 2008, based on daily compounding.

You can read Revenue Ruling 2008-54 announcing the new rates of interest.