The IRS has announced the interest rates for tax overpayments and underpayments for the calendar quarter beginning October 1, 2008.
For non-corporate taxpayers, the rate for both underpayments and overpayments will be 6%. For corporations, the overpayment rate will be 5%. Corporations will receive 3.5% for overpayments exceeding $10,000. The underpayment rate for corporations will be 6%, but will be 8% for large corporate underpayments.