section— (1) In general The tentative fair share tax for the taxable year is 30 percent of the excess of— (A) the adjusted gross income of the taxpayer, over (B) the modified charitable contribution deduction for the taxable year. (2) Modified charitable contribution deduction For purposes of paragraph (1)— (A) In general The modified charitable contribution deduction for any taxable year is an amount equal to the amount which bears the same ratio to the deduction allowable under section 170 (section 642(c) in the case of a trust or estate) for such taxable year as— (i) the amount of itemized deductions allowable under the regular tax (as defined in section 55) for such taxable year, determined after the application of section 68, bears to (ii) such amount, determined before the application of section 68. (B) Taxpayer must itemize In the case of any individual who does not elect to itemize deductions for the taxable year, the modified charitable contribution deduction shall be zero. (c) High-Income taxpayer For purposes of this section— (1) In general The term high-income taxpayer means, with respect to any taxable year, any taxpayer (other than a corporation) with an adjusted gross income for such taxable year in excess of $1,000,000 (50 percent of such amount in the case of a married individual who files a separate return). (2) Inflation adjustment (A) In general In the case of a taxable year beginning after 2018, the $1,000,000 amount under paragraph (1) shall be increased by an amount equal to— (i) such dollar amount, multiplied by (ii) the cost-of-living adjustment determined under section 1(f)(3) for the calendar year in which the taxable year begins, determined by substituting calendar year 2017 for calendar year 1992 in subparagraph (B) thereof. (B) Rounding If any amount as adjusted under subparagraph (A) is not a multiple of $10,000, such amount shall be rounded to the next lowest multiple of $10,000. (d) Payroll tax For purposes of this section, the payroll tax for any taxable year is an amount equal