For purposes of this part, a capital gain dividend is any dividend, or part thereof, which is designated by the real estate investment trust as a capital gain dividend in a written notice mailed to its shareholders or holders of beneficial interests at any time before the expiration of 30 days after the close of its taxable year (or mailed to its shareholders or holders of beneficial interests with its annual report for the taxable year); except that, if there is an increase in the excess described in subparagraph (A)(ii) of this paragraph for such year which results from a determination (as defined in section
860
(e)), such designation may be made with respect to such increase at any time before the expiration of 120 days after the date of such determination. If the aggregate amount so designated with respect to a taxable year of the trust (including capital gain dividends paid after the close of the taxable year described in section
858) is greater than the net capital gain of the taxable year, the portion of each distribution which shall be a capital gain dividend shall be only that proportion of the amount so designated which such net capital gain bears to the aggregate amount so designated. For purposes of this subparagraph, the amount of the net capital gain for any taxable year which is not a calendar year shall be determined without regard to any net capital loss attributable to transactions after December 31 of such year, and any such net capital loss shall be treated as arising on the 1st day of the next taxable year. To the extent provided in regulations, the preceding sentence shall apply also for purposes of computing the taxable income of the real estate investment trust.