Income Tax Act Article 14-6
When an individual fails to file the tax return specified in the preceding Article, or when, without due cause, the declared transaction price is lower than the prevailing market price, the tax authority may assess the transaction price, based on the prevailing market price or data obtained through investigation. When an individual fails to present the documents of evidence of the original cost, the tax authority may assess the cost, based on the data obtained through investigation; without the investigative information, the tax authority may assess the cost, based on the assessed value of the house and the present value of land at the time of acquisition (which shall be duly adjusted with the price index announced by the government). When an individual fails to present the expenses necessary for acquisition, improvement, and ownership transfer of the house and land, the tax authority may assess the expense, based on 3% of the transaction price, and such expense shall not exceed NT$300,000.
中文原文 所得稅法第14-6條
個人未依前條規定申報或申報之成交價額較時價偏低而無正當理由者，稽徵機關得依時價或查得資料，核定其成交價額；個人未提示原始取得成本之證明文件者，稽徵機關得依查得資料核定其成本，無查得資料，得依原始取得時房屋評定現值及公告土地現值按政府發布之消費者物價指數調整後，核定其成本；個人未提示因取得、改良及移轉而支付之費用者，稽徵機關得按成交價額百分之三計算其費用，並以三十萬元為限。