(B) and inserting $18,000 , and (2) by striking $3,000 in subparagraph (C) and inserting $12,000 . (b) Inflation adjustment Section 63(c)(4) is amended to read as follows: (4) Adjustments for inflation (A) In general In the case of a taxable year beginning after 2018, each dollar amount in paragraph (2)(B), (2)(C), or (5) or subsection (f) 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 for 2016 in subparagraph (A)(ii) thereof— (I) in the case of the dollar amounts contained in paragraph (2)(B) or (2)(C), 2017 , (II) in the case of the dollar amounts contained in paragraph (5)(A) or subsection (f), 1987 , and (III) in the case of the dollar amount contained in paragraph (5)(B), 1997 . (B) Rounding If any increase under subparagraph (A) is not a multiple of $50, such increase shall be rounded to the next lowest multiple of $50. . (c) Conforming amendments (1) Section 1(f)(7)(A) is amended by striking section 63(c)(4), . (2) Section 1(f)(7)(B) is amended by striking sections 63(c)(4) and and inserting section . (3) Section 63(c) is amended by striking paragraph (7). (d) Effective date The amendments made by this section shall apply to taxable years beginning after December 31, 2017. 122. Increase in and modification of child tax credit (a) In general Section 24 is amended by striking subsections (a), (b), and (c) and inserting the following new subsections: (a) Allowance of credit There shall be allowed as a credit against the tax imposed by this chapter for the taxable year an amount equal to the sum of— (1) $2,000 for each qualifying child of the taxpayer, and (2) $500 for each qualifying dependent (other than a qualifying child) of the taxpayer. (b) Limitation based on adjusted gross income The amount of the credit allowable under subsection (a) shall be reduced (but not below zero) by $50 for each $1,000 (or fraction thereof) by