The amount of an old-age insurance benefit (other than a benefit based on a primary insurance amount determined under section 415(a)(3) of this title as in effect in December 1978 or section 415(a)(1)(C)(i) of this title as in effect thereafter) which is payable without regard to this subsection to an individual shall be increased by—
(A) the applicable percentage (as determined under paragraph (6)) of such amount, multiplied by
(B) the number (if any) of the increment months for such individual.