5 CFR § 300.605 - Creditable service.
(a) All service at the required or higher grade (or equivalent) in positions to which appointed in the Federal civilian service is creditable towards the time periods required by § 300.604 of this part, except as provided in paragraph (c) of this section. Creditable service includes competitive and excepted service in positions under the General Schedule and other pay systems, including employment with a nonappropriated fund instrumentality. Service while on detail is credited at the grade of the employee's position of record, not the grade of the position to which detailed. Also creditable is service with the District of Columbia Government prior to January 1, 1980 (or prior to September 26, 1980, for those District employees who were converted to the District personnel system on January 1, 1980).
(b) Service in positions not subject to the General Schedule (GS) is credited at the equivalent GS grade by comparing the candidate's rate of basic pay with the representative rate (as defined in § 351.203 of this chapter) of the GS position in effect when the non-GS service was performed. The equivalent GS grade is the GS grade with a representative rate that equals the candidate's rate of basic pay. When the candidate's rate of basic pay falls between the representative rates of two GS grades, the non-GS service is credited at the higher grade.
(c) In applying the restrictions in § 300.604 of this part, prior service under temporary appointment at a level above that of a subsequent nontemporary competitive appointment is credited as if the service had been performed at the level of the nontemporary appointment. This provision applies until the employee has served in pay status for 52 weeks under nontemporary competitive appointment; thereafter, the service is credited at its actual grade level (or equivalent).