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.

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.

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.

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.

For extension of the period of limitation in case of an extension under subsection (a)(2) or subsection (b)(2), see section 6503(d).

For authority of the Secretary to require security in case of an extension under subsection (a)(2) or subsection (b), see section 6165.