20 C.F.R. § 404.230 – Guaranteed alternative.

(a) General. If you reach age 62 after 1978 but before 1984, we compute your primary insurance amount under a modified average-monthly-wage method as a guaranteed alternative to your primary insurance amount computed under the average-indexed-monthly-earnings method. We also compute your primary insurance amount under the old-start method (§§ 404.240 through 404.242) and under the special rules for a person who had a period of disability (§§ 404.250 through 404.252), if you are eligible. In §§ 404.231 through 404.233, we explain the average-monthly-wage method as the alternative to the average-indexed-monthly-earnings method.
(b) Restrictions.
1. (1) To qualify for this guaranteed-alternative computation, you must have some creditable earnings before 1979.
2. (2) You or your survivors do not qualify for a guaranteed-alternative computation if you were eligible (you attained age 62, became disabled, or died before age 62) for social security benefits based on your own earnings at any time before 1979 unless—
  1. (i) Those benefits were disability insurance benefits which were terminated because you recovered from your disability or you engaged in substantial gainful activity; and
  2. (ii) You spent at least 12 months without being eligible for disability benefits again.
3. (3) This guaranteed alternative method applies only to old-age insurance benefits and to survivor benefits where the deceased worker reached the month of his or her 62nd birthday after 1978 but before 1984 and died after reaching age 62.