20 C.F.R. § 404.315
(a) General. You are entitled to disability benefits while disabled before attaining full retirement age as defined in § 404.409 if—
(4) You have been disabled for 5 full consecutive months or no waiting period is required. The 5-month waiting period begins with a month in which you were both insured for disability and disabled. Your waiting period can begin no earlier than the 17th month before the month you apply—no matter how long you were disabled before then. No waiting period is required if:
[44 FR 34481, June 15, 1979, as amended at 48 FR 21930, May 16, 1983; 51 FR 10616, Mar. 28, 1986; 51 FR 16166, May 1, 1986; 53 FR 43681, Oct. 28, 1988; 57 FR 30119, July 8, 1992; 60 FR 8145, Feb. 10, 1995; 68 FR 4704, Jan. 30, 2003; 86 FR 48021, Aug. 27, 2021; 91 FR 16829, Apr. 3, 2026]