; special rules based on marital and filing status (1) Dollar limitation The credit allowed under subsection (a) shall not exceed $10,000. (2) Limitation based on purchase price The amount allowable as a credit under subsection (a) (determined without regard to this paragraph and paragraph (3), and after the application of paragraph (1)) for the taxable year shall be reduced (but not below zero) by the amount which bears the same ratio to the amount which is so allowable as— (A) the excess (if any) of— (i) the purchase price of the residence, over (ii) $600,000, bears to (B) $100,000. (3) Limitation based on modified adjusted gross income (A) In general The amount allowable as a credit under subsection (a) (determined without regard to this paragraph and after the application of paragraphs (1) and (2)) for the taxable year shall be reduced (but not below zero) by the amount which bears the same ratio to the amount which is so allowable as— (i) the excess (if any) of— (I) the taxpayer's modified adjusted gross income for such taxable year, over (II) $80,000 ($160,000 in the case of a joint return), bears to (ii) $20,000. (B) Modified adjusted gross income For purposes of subparagraph (A), the term modified adjusted gross income means the adjusted gross income of the taxpayer for the taxable year increased by any amount excluded from gross income under section 911, 931, or 933. (4) Age limitation No credit shall be allowed under subsection (a) with respect to the purchase of any residence for a taxable year if— (A) the taxpayer has not attained age 18 as of the date of such purchase, or (B) a deduction under section 151 with respect to the taxpayer is allowable to another taxpayer for the taxable year. In the case of a taxpayer who is married, the taxpayer shall be treated as meeting the age requirement of subparagraph (A) if the taxpayer or the taxpayer's spouse meets such age requirement. (5) Multiple purchasers If two or more individuals who are not married purchase a principal residence, the amount of the