26 CFR § 1.669(a)-1 - Limitation on tax.
(a) In general. Section 669 provides that, at the election of a beneficiary who is a U.S. person (as defined in section 7701(a)(30)) and who satisfies the requirements of section 669(b) (that certain information with respect to the operation and accounts of the trust be supplied), the tax attributable to the amounts treated under section 668(a) as having been received by him, from a foreign trust created by a U.S. person, on the last day of a preceding taxable year of the trust shall not be greater than the tax computed under section 669(a)(1)(A) (the computation under this provision will hereinafter be referred to as the “exact throwback” method) or under section 669(a)(1)(B) (the computation under this provision will hereinafter be referred to as the “short-cut throwback” method). This election of the beneficiary with respect to the taxable year of the beneficiary in which the distribution is made shall be made with the district director before the expiration of the period of limitations for assessment provided in section 6501 for such taxable year.
(b) Where no election is made. If the beneficiary does not make the election provided in section 669(a) in the manner required in section 669(b) and § 1.669(b)-2, or furnish the information with respect to the operation and accounts of the foreign trust created by a U.S. person required by section 669(b) and § 1.669(b)-1, the tax on an accumulation distribution treated under section 668(a) as having been received by him from such foreign trust on the last day of a preceding taxable year of the trust shall be computed without reference to section 668 or 669. In such case, the entire accumulation distribution will be included in the gross income of the beneficiary in the year in which it is paid, credited, or required to be distributed, and tax for such year will be computed on the basis of the beneficiary's total taxable income for the year after taking into account such inclusion in gross income.
(c) Year for which tax is payable. The tax, regardless of the manner in which computed, of the beneficiary which is attributable to an accumulation distribution is imposed on the beneficiary for the taxable year of the beneficiary in which the accumulation distribution is made to him unless the taxable year of the beneficiary is different from that of the trust. See section 662(c) and § 1.662(c)-1.