Enforcement Rules of the Income Tax Act Article 3-2

When the trustee calculates various income amounts of the beneficiary in accordance with Paragraph 1, Article 3-4 of the Act, the trustee accounting system may adopt either a cash or accrual basis, which shall not be changed once determined. The term for income calculation shall commence on the first day of January and end on the thirty-first day of December of each calendar year.When the trustee calculates various income amounts of the trust property in accordance with Article 3-4 of the Act, the related costs, necessary expenses and losses shall be deducted from entries under corresponding income categories in accordance with the proportion of amounts under various income categories to the gross income derived from the trust property, except for what can be directly, reasonably and clearly categorized that may be individually categorized, recognized and deducted.
中文原文 所得稅法施行細則第3-2條
受託人依本法第三條之四第一項規定計算受益人之各類所得額時,得採用現金收付制或權責發生制,一經選定不得變更。
計算所得之起訖期間,應為每年一月一日起至十二月三十一日止。
受託人依本法第三條之四規定計算信託財產之各類所得額時,其相關之成本、必要費用或損耗,除可直接合理明確歸屬者,得個別歸屬認列減除外,應按信託財產發生之各該所得類別之收入金額占其總收入之比例分攤,自各該所得類別收入項下減除。

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