26 USC 11 - Tax imposed

(a) Corporations in general 
A tax is hereby imposed for each taxable year on the taxable income of every corporation.
(b) Amount of tax 

(1) In general 
The amount of the tax imposed by subsection (a) shall be the sum of
(A) 15 percent of so much of the taxable income as does not exceed $50,000,
(B) 25 percent of so much of the taxable income as exceeds $50,000 but does not exceed $75,000,
(C) 34 percent of so much of the taxable income as exceeds $75,000 but does not exceed $10,000,000, and
(D) 35 percent of so much of the taxable income as exceeds $10,000,000.

In the case of a corporation which has taxable income in excess of $100,000 for any taxable year, the amount of tax determined under the preceding sentence for such taxable year shall be increased by the lesser of (i) 5 percent of such excess, or (ii) $11,750. In the case of a corporation which has taxable income in excess of $15,000,000, the amount of the tax determined under the foregoing provisions of this paragraph shall be increased by an additional amount equal to the lesser of (i) 3 percent of such excess, or (ii) $100,000.

(2) Certain personal service corporations not eligible for graduated rates 
Notwithstanding paragraph (1), the amount of the tax imposed by subsection (a) on the taxable income of a qualified personal service corporation (as defined in section 448 (d)(2)) shall be equal to 35 percent of the taxable income.
(c) Exceptions 
Subsection (a) shall not apply to a corporation subject to a tax imposed by
(1) section 594 (relating to mutual savings banks conducting life insurance business),
(2) subchapter L (sec. 801 and following, relating to insurance companies), or
(3) subchapter M (sec. 851 and following, relating to regulated investment companies and real estate investment trusts).
(d) Foreign corporations 
In the case of a foreign corporation, the taxes imposed by subsection (a) and section 55 shall apply only as provided by section 882.