5 CFR §870.505

1. (a)An insured individual may cancel entirely any type of Optional insurance, or reduce the number of multiples of his/her Option B insurance, at any time by filing a waiver of Optional insurance coverage. An employee files with the employing office. An annuitant files with OPM or other office that administers his/her retirement system. If still employed, a compensationer files with the employing office, and if not still employed, with OPM. Exception: an individual who has assigned his/her insurance under subpart I of this part cannot cancel Option A or Option B coverage.
2. (b)A cancellation of Optional insurance becomes effective, and Optional insurance stops, at the end of the pay period in which the waiver is properly filed. Exception: if Option C is cancelled because there are no eligible family members, the effective date is retroactive to the end of the pay period in which there stopped being any eligible family members.
3. (c)A waiver of Optional insurance remains in effect until it is cancelled as provided in § 870.506.