Enforcement Rules of the Income Basic Tax Act Article 9
When calculating the securities transaction income of a profit-seeking enterprise under the provisions set out in Subparagraph 1, Article 7 of the Act, except for the attributable operating expenses and loan interests which may be attributed separately to applicable accounts for book-keeping purposes, all other expenses and interests amortized to the sale of negotiable securities while calculating the transaction cost under the relevant provisions set out in the Income Tax Act may be deducted from the business income derived from the selling of such negotiable securities.
中文原文 所得基本稅額條例施行細則第9條
營利事業於計算本條例第七條第一項第一款所定之證券交易所得時，其營業費用及借款利息，除可合理明確歸屬者，得個別歸屬認列外，其依所得稅法相關規定計算之出售有價證券應分攤之費用及利息，得自有價證券出售收入項下減除。