20 CFR §404.120

1. (a)What the period is for determining currently insured status. You are currently insured if you have at least 6 quarters of coverage (QCs) during the 13-quarter period ending with the quarter in which you—
   1. (1)Die;
   2. (2)Most recently became entitled to disability insurance benefits; or
   3. (3)Became entitled to old-age insurance benefits.
2. (b)What quarters are not counted as part of the 13-quarter period. We do not count as part of the 13-quarter period any quarter all or part of which is included in a period of disability established for you, except that the first and last quarters of the period of disability may be counted if they are QCs (see § 404.146(d)).