(1) Capital gains and capital losses, other than gains and losses on securities issued by the government of the United States, shall be included in income only to the extent of that portion of the gains or losses which occur after the effective date of this ordinance. In determining the amount of gain or loss, the taxpayer may use net proceeds from the sale or exchange less fair market value as of the effective date of this ordinance. The fair market value of property shall be determined by an appraisal or similar reliable evidence. The fair market value of a security shall be the last quoted price on the last business day prior to the effective date. For a security traded over the counter the last quoted price shall be the last bid price on the last business day prior to the effective date. The taxpayer may determine the gain or loss on a transaction in the same manner as for federal income tax purposes taking into account only that portion thereof which occurs after the effective date. The portion of that gain or loss includible in computing taxable income will be the same proportion of the total gain or loss as the period of time the property was held after the effective date of the ordinance bears to the total time the property was held. In any city adopting this ordinance which had a valid local income tax ordinance in effect on January 1, 1964, capital gains and losses shall be included to the extent of that portion of such gains or losses which occur after the effective date of the original city income tax ordinance.

    (2) If capital losses exceed capital gains in a taxable year, the unused portion may be utilized to the same extent and on the same basis as under the federal internal revenue code.