From IRS.gov

WASHINGTON ? The Internal Revenue Service today announced that interest rates will remain the same for the calendar quarter beginning Jan. 1, 2018. The rates will be: 
 

four (4) percent for overpayments [three (3) percent in the case of a corporation];

1 and one-half (1.5) percent for the portion of a corporate overpayment exceeding $10,000;

four (4) percent for underpayments; and

six (6) 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 Oct. 2017 to take effect Nov. 1, 2017, based on daily compounding.

Revenue Ruling 2017-25, announcing the rates of interest, is attached and will appear in Internal Revenue Bulletin 2017-52, dated Dec. 26, 2017. 

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