(a) Basis for computation.

(1) The beneficiary's income and tax paid for any prior taxable year for which a recomputation is involved under either the exact method or the short-cut method shall be determined by reference to the information required to be furnished by him under §1.668(b)-4A(a). The gross income, related deductions, and taxes paid for a prior taxable year of the beneficiary as finally determined shall be used for computation purposes. The term “as finally determined” has reference to the final status of the gross income, deductions, credits, and taxes of the taxable year after the expiration of the period of limitations or after completion of any court action regarding the tax for the taxable year.

(2) If any computations rely on the beneficiary's return for a prior taxable year for which the applicable period of limitations on assessment under section 6501 has expired, and such return shows a mathematical error on its face which resulted in the wrong amount of tax being paid for such year, the determination of both the tax for such year computed with the inclusion of the section 666 amount in the beneficiary's gross income and the tax for such year computed without including such amounts in such gross income shall be based upon the return after the correction of such mathematical errors, and the beneficiary shall be credited for the correct amount of tax that should have been properly paid.

(b) Effect of allocation of undistributed net income on items based on amount of income and with respect to a net operating loss, a charitable contributions carryover, or a capital loss carryover.

(1) In computing the tax for any taxable year under either the exact method or the short-cut method, any item which depends upon the amount of gross income, adjusted gross income, or taxable income shall be recomputed to take into consideration the amount of undistributed net income allocated to such year. For example, if $1,000 of undistributed net income is allocated to 1970, adjusted gross income for 1970 is increased from $5,000 to $6,000. The allowable 50 percent charitable deduction under section 170(b)(1)(A) is then increased and the amount of the nondeductible medical expenses under section 213 (3 percent of adjusted gross income) is also increased.

(2) In computing the tax attributable to the undistributed net income deemed distributed to the beneficiary in any of his prior taxable years under either the exact method or the short-cut method, the effect of amounts of undistributed net income on a net operating loss carryback or carryover, a charitable contributions carryover, or a capital loss carryback or carryover, shall be taken into account. In determining the amount of tax attributable to such deemed distribution, a computation shall also be made for any taxable year which is affected by a net operating loss carryback or carryover, by a charitable contributions carryover, or by a capital loss carryback or carryover determined by reference to the taxable year to which amounts are allocated under either method and which carryback or carryover is reduced or increased by such amounts so allocated. The provisions of this subparagraph may be illustrated by the following example:

(c) Averaging. A beneficiary who uses the exact method may recompute his tax for a prior taxable year by using income averaging for all of his actual income for that year, plus the amount deemed distributed in that year under section 666, even though he may not have actually used section 1301 to determine his income tax for such taxable year. For purposes of such recomputation, the beneficiary's income for all other taxable years involved must include any amounts deemed distributed in such years from the current and all prior accumulation distributions. See §1.668(b)-4A(c)(3) for additional information requirements. The beneficiary may not apply the provisions of this paragraph to a taxable year in which an amount is deemed to be income by reason of §1.666(d)-1A(b). The accumulation distribution itself is not eligible for income averaging in the years in which it is paid, credited, or required to be distributed. See section 1302 (a)(2)(B) and the regulations thereunder.

[T.D. 7204, 37 FR 17151, Aug. 25, 1972]