26 U.S.C. § 6664 — Definitions and special rules

Source [1] 26 U.S.C. § 6664 — Definitions and special rules

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“(c) Reasonable cause exception for underpayments (c) Reasonable cause exception for underpayments › (1) In general No penalty shall be imposed under section 6662 or 6663 with respect to any portion of an underpayment if it is shown that there was a reasonable cause for such portion and that the taxpayer acted in good faith with respect to such portion.”

> Official source: https://uscode.house.gov/quicksearch/get.plx?title=26&section=6664 — Internal Revenue Code text as published by the U.S. House Office of the Law Revision Counsel, USLM bulk release point 119-102, retrieved 2026-09-09. Cite as: IRC § 6664. **Statutory text only** — editorial notes, amendment history and effective-date notes are omitted; confirm currency for amendments after the release point.

(a) Underpayment › (1) For purposes of this part, the term “underpayment” means the amount by which any tax imposed by this title exceeds the excess of—

(1)

the sum of— (A) the amount shown as the tax by the taxpayer on his return, plus (B) amounts not so shown previously assessed (or collected without assessment), over

(a) Underpayment › (2) the amount of rebates made.

For purposes of paragraph (2), the term “rebate” means so much of an abatement, credit, refund, or other repayment, as was made on the ground that the tax imposed was less than the excess of the amount specified in paragraph (1) over the rebates previously made. A rule similar to the rule of section 6211(b)(4) shall apply for purposes of this subsection.

(c) Reasonable cause exception for underpayments The penalties provided in this part shall apply only in cases where a return of tax is filed (other than a return prepared by the Secretary under the authority of section 6020(b)).

(c) Reasonable cause exception for underpayments › (1) In general No penalty shall be imposed under section 6662 or 6663 with respect to any portion of an underpayment if it is shown that there was a reasonable cause for such portion and that the taxpayer acted in good faith with respect to such portion.

(c) Reasonable cause exception for underpayments › (2) Exception Paragraph (1) shall not apply to any portion of an underpayment which is attributable to one or more transactions described in section 6662(b)(6) or to any disallowance of a deduction described in section 6662(b)(10).

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