The Taxpayer Rights Protection Act Article 14
When tax authorities are unable to determine the tax base after investigation, or the investigation costs are disproportionally expensive, tax estimation is allowed for the principle of upholding tax equity, and the basis for estimation and the calculation information shall be stated in writing.Tax estimation made by tax authorities shall consider all material items relevant to estimation through reasonable and objective procedures and appropriate means.Estimation shall be done by the means which is nearest the actual amount when more than two means exist.In the cases that taxpayers have already fulfilled their obligation to facilitate investigation by reporting the required information, tax authorities shall not impose a penalty according to the estimation results.
中文原文 納稅者權利保護法第14條
稅捐稽徵機關對於課稅基礎，經調查仍不能確定或調查費用過鉅時，為維護課稅公平原則，得推計課稅，並應以書面敘明推計依據及計算資料。
稅捐稽徵機關推計課稅，應斟酌與推計具有關聯性之一切重要事項，依合理客觀之程序及適切之方法為之。
推計，有二種以上之方法時，應依最能切近實額之方法為之。
納稅者已依稅法規定履行協力義務者，稅捐稽徵機關不得依推計結果處罰。
稅捐稽徵機關推計課稅，應斟酌與推計具有關聯性之一切重要事項，依合理客觀之程序及適切之方法為之。
推計，有二種以上之方法時，應依最能切近實額之方法為之。
納稅者已依稅法規定履行協力義務者，稅捐稽徵機關不得依推計結果處罰。