Taxable year to be used in determining modified adjusted gross income

In applying this subsection for an individual’s premiums in a month in a year, subject to clause (ii) and subparagraph (C), the individual’s modified adjusted gross income shall be such income determined for the individual’s last taxable year beginning in the second calendar year preceding the year involved.

If, as of October 15 before a calendar year, the Secretary of the Treasury does not have adequate data for an individual in appropriate electronic form for the taxable year referred to in clause (i), the individual’s modified adjusted gross income shall be determined using the data in such form from the previous taxable year. Except as provided in regulations prescribed by the Commissioner of Social Security in consultation with the Secretary, the preceding sentence shall cease to apply when adequate data in appropriate electronic form are available for the individual for the taxable year referred to in clause (i), and proper adjustments shall be made to the extent that the premium adjustments determined under the preceding sentence were inconsistent with those determined using such taxable year.

In the case of individuals with respect to whom the Secretary of the Treasury does not have adequate data in appropriate electronic form for either taxable year referred to in clause (i) or clause (ii), the Commissioner of Social Security, in consultation with the Secretary, shall prescribe regulations which provide for the treatment of the premium adjustment with respect to such individual under this subsection, including regulations which provide for—

(I) the application of the highest applicable percentage under paragraph (3)(C) to such individual if the Commissioner has information which indicates that such individual’s modified adjusted gross income might exceed the threshold amount for the taxable year referred to in clause (i), and

(II) proper adjustments in the case of the application of an applicable percentage under subclause (I) to such individual which is inconsistent with such individual’s modified adjusted gross income for such taxable year.