Enforcement Rules of the Negotiable Instruments Act Article 9

Interest required to be deducted pursuant to Article 65, paragraph 3 of the Act shall be deducted at the agreed interest rate, if any. If no rate has been agreed upon, the interest shall be deducted at the rate specified in Article 28, paragraph 2 of the Act.
中文原文 票據法施行細則第9條
依本法第六十五條第三項規定,應扣減之利息,其有約定利率者,依約定利率扣減,未約定利率者,依本法第二十八條第二項規定之利率扣減。

English translation for reference only; the Chinese text prevails. Not legal advice.