5 CFR § 550.708 - Creditable service.
The following types of service are creditable for computing an employee's severance pay under § 550.707:
(a) Civilian service as an employee (as defined in 5 U.S.C. 2105), excluding time during a period of nonpay status that is not creditable for annual leave accrual purposes under 5 U.S.C. 6303(a);
(b) Service performed with the United States Postal Service or the Postal Rate Commission;
(c) Military service, including active or inactive training with the National Guard, when performed by an employee who returns to civilian service through the exercise of a restoration right provided by law, Executive order, or regulation;
(d) Service performed by an employee of a nonappropriated fund instrumentality of the Department of Defense or the Coast Guard, as defined in 5 U.S.C. 2105(c), who moves to a position within the civil service employment system of the Department of Defense or the Coast Guard, respectively, without a break in service of more than 3 days; and
(e) Service performed with the government of the District of Columbia by an individual first employed by that government before October 1, 1987, excluding service as a teacher or librarian of the public schools of the District of Columbia.