(a) Civilian employees may elect to contribute a percentage of basic pay or a dollar amount, subject to the limits described in § 1600.22. The election must be expressed in whole percentages or whole dollar amounts. A participant may contribute a percentage for one type of contribution and a dollar amount for another type of contribution. If a participant elects to contribute a dollar amount to his or her traditional balance and a dollar amount to his or her Roth balance, but the total dollar amount elected is more than the amount available to be deducted from the participant's basic pay, the employing agency will deduct traditional contributions first and Roth contributions second.

(b) Uniformed services members may elect to contribute from basic pay and, if they elect to contribute from basic pay, special or incentive pay (including bonus pay) subject to the limits described in § 1600.22. The election may be expressed as a whole percentage, a dollar amount, or both as determined by the member's service.