20 C.F.R. § 404.143
(a) Crediting quarters of coverage (QCs). For calendar years after 1977, we credit you with a QC for each part of the total wages paid and self-employment income credited (under § 404.144) to you in a calendar year that equals the amount required for a QC in that year. For example, if the total of your wages and self-employment income for a calendar year is more than twice, but less than 3 times, the amount required for a QC in that year, we credit you with only 2 QCs for the year. The rules for crediting QCs in this section are subject to the limitations in § 404.146, which tells when a calendar quarter cannot be a QC. In addition, we cannot credit you with more than four QCs for any calendar year. The amount of wages and self-employment income that you must have for each QC is—
(b) Assigning QCs. We assign a QC credited under paragraph (a) of this section to a specific calendar quarter in the calendar year only if the assignment is necessary to—
[45 FR 25834, Apr. 15, 1980, as amended at 62 FR 38450, July 18, 1997]