Income Tax Act Article 44

Inventories of merchandise, raw materials, supplies, goods-in-process, finished goods and by-products shall be evaluated on the basis of actual cost. Where the cost is higher than the net realizable value, the taxpayer may take the net realizable value as the basis of evaluation. A loss on a decline in the net realizable value of the inventories is allowed to be the cost of goods sold. In case the cost is not ascertainable or the net realizable value is not derivable by reasonable anticipation, the competent tax authority shall determine it on the basis of expert opinion or by appraisal.Net realizable value as provided in the preceding paragraph refers to the expected net margin from the sales under regular operation.Cost as provided in Paragraph 1 may be calculated by using the specific identification method, first-in first-out method, weighted average method, moving average method, or other methods approved by the competent authority in accordance with the categories or characteristics of an inventory.
中文原文 所得稅法第44條
商品、原料、物料、在製品、製成品、副產品等存貨之估價,以實際成本為準;成本高於淨變現價值時,納稅義務人得以淨變現價值為準,跌價損失得列銷貨成本;成本不明或淨變現價值無法合理預期時,由該管稽徵機關用鑑定或估定方法決定之。
前項所稱淨變現價值,指營利事業預期正常營業出售存貨所能取得之淨額。
第一項成本,得按存貨之種類或性質,採用個別辨認法、先進先出法、加權平均法、移動平均法或其他經主管機關核定之方法計算之。

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