(A) General rule. The amount to be returned to the employer is the excess of the amount contributed or paid over the amount that would have been contributed or paid had no mistake been made. This amount is the excess contribution or overpayment. Except as provided in
paragraph (b)(2)(ii)(B) of this section, interest or earnings attributable to an excess contribution shall not be returned to the employer, and any losses attributable to an excess contribution must reduce the amount returned to the employer. For purposes of the previous sentence, the application of plan-wide investment experience to the excess contribution would be an acceptable method of calculating losses. A refund of a mistaken contribution must in no event reduce a participant's account balance in a defined contribution plan to an amount less than that amount which would properly have been in that participant's account had no mistake occurred. Thus, to the extent that the refund of an excess contribution would reduce a participant's account balance in a defined contribution plan to an amount less than the amount which would properly be in the participant's account had no mistake occurred, the return of the excess contribution would be prohibited by this section.