26 CFR § 1.165-4 - Decline in value of stock.
(a) Deduction disallowed. No deduction shall be allowed under section 165(a) solely on account of a decline in the value of stock owned by the taxpayer when the decline is due to a fluctuation in the market price of the stock or to other similar cause. A mere shrinkage in the value of stock owned by the taxpayer, even though extensive, does not give rise to a deduction under section 165(a) if the stock has any recognizable value on the date claimed as the date of loss. No loss for a decline in the value of stock owned by the taxpayer shall be allowed as a deduction under section 165(a) except insofar as the loss is recognized under § 1.1002-1 upon the sale or exchange of the stock and except as otherwise provided in § 1.165-5 with respect to stock which becomes worthless during the taxable year.
(b) Stock owned by banks.
(1) In the regulation of banks and certain other corporations, Federal and State authorities may require that stock owned by such organizations be charged off as worthless or written down to a nominal value. If, in any such case, this requirement is premised upon the worthlessness of the stock, the charging off or writing down will be considered prima facie evidence of worthlessness for purposes of section 165(a); but, if the charging off or writing down is due to a fluctuation in the market price of the stock or if no reasonable attempt to determine the worthlessness of the stock has been made, then no deduction shall be allowed under section 165(a) for the amount so charged off or written down.
(2) This paragraph shall not be construed, however, to permit a deduction under section 165(a) unless the stock owned by the bank or other corporation actually becomes worthless in the taxable year. Such a taxpayer owning stock which becomes worthless during the taxable year is not precluded from deducting the loss under section 165(a) merely because, in obedience to the specific orders or general policy of such supervisory authorities, the value of the stock is written down to a nominal amount instead of being charged off completely.
(c) Application to inventories. This section does not apply to a decline in the value of corporate stock reflected in inventories required to be taken by a dealer in securities under section 471. See § 1.471-5.
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