Amount of the penalty.
Amount of the penalty. The amount of the penalty shall be equal to -
(1) Five percent of the deficiency (or imputed underpayment) if the failure is for not more than one month; plus
(2) An additional five percent of the deficiency (or imputed underpayment) for each month (or fraction thereof) during which the failure continues, but not to exceed in the aggregate twenty-five percent of the deficiency (or imputed underpayment).
26 CFR § 301.6689-1
Application of civil penalty. If a foreign tax redetermination occurs, and the taxpayer failed to notify the Internal Revenue Service (IRS) on or before the date and in the manner prescribed in 1.905-4 of this chapter, or as required under section 404A(g)(2), for giving notice of a foreign tax redetermination, then, unless paragraph (d) of this section applies, there is added to the deficiency (or the imputed underpayment as determined under section 6225) attributable to such redetermination an amount determined under paragraph (b) of this section. Subchapter B of chapter 63 of the Internal Revenue Code (relating to deficiency proceedings) does not apply with respect to the assessment of the amount of the penalty.