26 U.S.C. § 6161

(a) Amount determined by taxpayer on return (1) General rule The Secretary, except as otherwise provided in this title, may extend the time for payment of the amount of the tax shown, or required to be shown, on any return or declaration required under authority of this title (or any installment thereof), for a reasonable period not to exceed 6 months (12 months in the case of estate tax) from the date fixed for payment thereof. Such extension may exceed 6 months in the case of a taxpayer who is abroad. (2) Estate tax The Secretary may, for reasonable cause, extend the time for payment of— (A) any part of the amount determined by the executor as the tax imposed by chapter 11, or (B) any part of any installment under section 6166 (including any part of a deficiency prorated to any installment under such section). for a reasonable period not in excess of 10 years from the date prescribed by section 6151(a) for payment of the tax (or, in the case of an amount referred to in subparagraph (B), if later, not beyond the date which is 12 months after the due date for the last installment). (b) Amount determined as deficiency (1) Income, gift, and certain other taxes Under regulations prescribed by the Secretary, the Secretary may extend the time for the payment of the amount determined as a deficiency of a tax imposed by chapter 1, 12, 41, 42, 43, or 44 for a period not to exceed 18 months from the date fixed for the payment of the deficiency, and in exceptional cases, for a further period not to exceed 12 months. An extension under this paragraph may be granted only where it is shown to the satisfaction of the Secretary that payment of a deficiency upon the date fixed for the payment thereof will result in undue hardship to the taxpayer in the case of a tax imposed by chapter 1, 41, 42, 43, or 44, or to the donor in the case of a tax imposed by chapter 12. (2) Estate tax Under regulations prescribed by the Secretary, the Secretary may, for reasonable cause, extend the time for the payment of any deficiency of a tax imposed by chapter 11 for a reasonable period not to exceed 4 years from the date otherwise fixed for the payment of the deficiency. (3) No extension for certain deficiencies No extension shall be granted under this subsection for any deficiency if the deficiency is due to negligence, to intentional disregard of rules and regulations, or to fraud with intent to evade tax. (c) Claims in cases under title 11 of the United States Code or in receivership proceedings Extensions of time for payment of any portion of a claim for tax under chapter 1 or chapter 12, allowed in cases under title 11 of the United States Code or in receivership proceedings, which is unpaid, may be had in the same manner and subject to the same provisions and limitations as provided in subsection (b) in respect of a deficiency in such tax. (d) Cross references (1) Period of limitation For extension of the period of limitation in case of an extension under subsection (a)(2) or subsection (b)(2), see section 6503(d). (2) Security For authority of the Secretary to require security in case of an extension under subsection (a)(2) or subsection (b), see section 6165. (3) Postponement of certain acts For time for performing certain acts postponed by reason of war, see section 7508, and by reason of Presidentially declared disaster or terroristic or military action, see section 7508A.