The amount of such benefit for the month in which an application for benefits becomes effective (or, if the Commissioner of Social Security so determines, for such month and the following month) and for any month immediately following a month of ineligibility for such benefits (or, if the Commissioner of Social Security so determines, for such month and the following month) shall—

(A) be determined on the basis of the income of the individual and the eligible spouse, if any, of such individual and other relevant circumstances in such month; and

(B) in the case of the first month following a period of ineligibility in which eligibility is restored after the first day of such month, bear the same ratio to the amount of the benefit which would have been payable to such individual if eligibility had been restored on the first day of such month as the number of days in such month including and following the date of restoration of eligibility bears to the total number of days in such month.