20 CFR 404.142: How we credit self-employment income to calendar quarters for taxable years beginning before 1978.

In crediting quarters of coverage under § 404.141(b)(2), we credit any self-employment income you derived during a taxable year that began before 1978 to calendar quarters as follows:

(a) If your taxable year was a calendar year, we credit your self-employment income equally to each quarter of that calendar year.

(b) If your taxable year was not a calendar year (that is, it began on a date other than January 1, or was less than a calendar year), we credit your self-employment income equally—

(1) To the calendar quarter in which your taxable year ended; and

(2) To each of the next three or fewer preceding quarters that were wholly or partly in your taxable year.