5 CFR §1600.23

1. (a)A participant may make traditional catch-up contributions or Roth catch-up contributions from basic pay at any time during the calendar year if he or she:
   1. (1)Is at least age 50 by the end of the calendar year;
   2. (2)Is making employee contributions at a rate that will result in the participant making the maximum employee contributions permitted under § 1600.22; and
   3. (3)Does not exceed the annual limit on catch-up contributions contained in section 414(v) the Internal Revenue Code.
2. (b)[Reserved]
3. (c)A participant may make traditional catch-up contributions and Roth catch-up contributions during the same year, but the combined total amount of catch-up contributions of both types cannot exceed the applicable Internal Revenue Code catch-up contribution limit for the year.
4. (d)A participant who has both a civilian account and a uniformed services account may make catch-up contributions to both accounts, but the combined total amount of catch-up contributions to both accounts cannot exceed the Internal Revenue Code catch-up contribution limit for the year.
5. (e)A participant cannot make catch-up contributions to his or her traditional balance from pay which is exempt from taxation under 26 U.S.C. 112.
6. (f)A participant may make catch-up contributions to his or her Roth balance from pay which is exempt from taxation under 26 U.S.C. 112.
7. (g)A participant cannot make catch-up contributions from special or incentive pay (including bonus pay).
8. (h)[Reserved]