20 CFR 229.42: When a child can no longer be included in computing an annuity rate under the overall minimum.

A child's inclusion in the computation of the overall minimum rate ends the earlier of:

(a) The month before the month in which the child dies; or

(b) The month before the month in which the child marries; or

(c) The month before the month the child becomes 18 years old, unless the child is disabled or a full-time student, as shown in part 216 of this chapter; or

(d) The second month after the month the child's disability ends, if the child is 18 years old or older, and not a full-time student; or

(e) The month in which a student child's annuity would end, as shown in part 218 of this chapter, if the child is 18 years old or older, a full-time student in an elementary or secondary school, and not disabled; or

(f) The month before the month the child becomes entitled to an overall minimum benefit or child's annuity on another earning record, if including the child on the other earnings record would result in higher monthly benefits; or

(g) In the case of a stepchild of the employee, the month after the month in which the divorce between the stepparent and the natural parent becomes final.