IRC § 41(g) – Special rule for pass-thru of credit
In the case of an individual who—
(1) owns an interest in an unincorporated trade or business,
(2) is a partner in a partnership,
(3) is a beneficiary of an estate or trust, or
(4) is a shareholder in an S corporation, the amount determined under subsection (a) for any taxable year shall not exceed an amount (separately computed with respect to such person’s interest in such trade or business or entity) equal to the amount of tax attributable to that portion of a person’s taxable income which is allocable or apportionable to the person’s interest in such trade or business or entity. If the amount determined under subsection (a) for any taxable year exceeds the limitation of the preceding sentence, such amount may be carried to other taxable years under the rules of section 39; except that the limitation of the preceding sentence shall be taken into account in lieu of the limitation of section 38 (c) in applying section 39. 
