20 C.F.R. § 218.6
(a) When application is filed. The applicant may choose an annuity beginning date by—
(b) After application is filed. After an application is filed, the claimant may choose an annuity beginning date by submitting a signed statement which tells the month, day and year when the annuity should begin.
(Approved by the Office of Management and Budget under control numbers 3220-0002, 3220-0030 and 3220-0042)