(a) In general. In computing taxable investment income for the taxable year, the gross amount of income from interest, the deduction under section 822(c)(1) for wholly tax-exempt interest, and the deduction under section 242 for partially tax-exempt interest, are, under the provisions of section 822(d)(2), each to be decreased by the appropriate amortization of premium and increased by the appropriate accrual of discount attributable to the taxable year on bonds, notes, debentures, or other evidences of indebtedness held by a mutual insurance company subject to the tax imposed by section 821 (a) or (c). However, only the accrual of discount relating to issue discount will increase the deduction for wholly tax-exempt interest. See section 103. Such amortization and accrual is the same as that provided for life insurance companies by section 818(b)(1), as amended by the Life Insurance Company Income Tax Act of 1959 (73 Stat. 133), and shall be determined in accordance with paragraphs (a) and (b) of § 1.818-3, except as provided by paragraph (b) of this section.

(b) Modifications. (1) Paragraph (b) of § 1.818-3 shall apply to mutual casualty insurance companies subject to the tax imposed by section 821 (a) or (c) without regard to the date of acquisition of the particular securities to which the amortization of premium or accrual of discount is attributable.

(2) In computing the amount of premium or discount for purposes of section 822(d)(2) with respect to securities held by a company taxable under section 821, the basis provided by section 1012 shall be used in lieu of the acquisition value provided by paragraph (b) of § 1.818-3. In the case of a company subject to the tax imposed by section 821(c), adjustments to basis to reflect the accrual of discount and the amortization of premium shall be made in the manner provided by paragraphs (a) and (b) of § 1.818-3. However, for purposes of determining statutory underwriting income or loss for the taxable year under section 823, a company subject to the tax imposed by section 821(a) is not required to accrue discount or to amortize premium in computing its income under section 832 as if it were subject to the tax imposed by section 831. Thus, the accrual of discount and amortization of premium required in the computation of taxable investment income by a company subject to the tax imposed by section 821(a) neither increases nor decreases the mutual insurance company taxable income of such a company and, except to the extent such a company actually accrues discount or amortizes premium for purposes of making the section 832 computation, no adjustment shall be made to the basis of obligations held by it to reflect accrual of discount or amortization of premium.