to the amount of such deductions (as so determined) as— (A) the excess of— (i) the taxpayer’s modified adjusted gross income for such taxable year, over (ii) $200,000 ($400,000 in the case of a joint return), bears to (B) $50,000 ($100,000 in the case of a joint return). (2) Modified adjusted gross income For purposes of this subsection, the term modified adjusted gross income means the adjusted gross income of the taxpayer (as defined in section 62 of the Internal Revenue Code of 1986) for the taxable year increased by any amount excluded from gross income under sections 911, 931, and 933 of such Code.