營業稅為「加值型」營業稅，有關納稅義務之發生及金額，應依營業稅法第15 條第1 項規定決定之。同法施行細則第29 條關於進項稅額未於當期申報者，得延後申報之規定，僅係為徵納雙方簡化稽徵程序，提升效率而設，並不得變更實體法納稅義務規定，以免影響納稅人權益。有關營業稅所漏稅額之計算，應回歸母法第15 條規定，納稅義務人之當期進項稅額未於當期申報者，仍應准予在稽徵機關在進行調查時嗣後補報，以便「正確」計算「客觀」的所漏稅額。釋字第660 號解釋不准納稅人嗣後補報扣抵進項稅額之作法，將虛增納稅人之當期「客觀應納稅額」，且實質上變成僅以當期「銷項稅額」作為所漏稅額，進行處罰計算基礎，不符「加值型」之制度精神，不僅有違課稅要件法定原則，也不符合實質課稅原則與量能課稅原則，更牴觸現代法治國家「有疑，則為有利被告認定之原則」。在釋字第660 號解釋未變更之前，宜採限縮解釋其適用範圍，對於下列特殊類型，基於憲法上比例原則以及量能課稅原則，仍應准予進項稅額之扣抵或推計課稅方式推估進項稅額並准予扣抵，以實現稅捐正義：因為不可歸責的事由導致帳證滅失的情形，或如不承認進項稅額之推計扣抵，將產生顯失公平之嚴苛結果的情形。例如未辦營業登記而營業，因此完全未依據規定取得進項憑證的情形，以及在借牌營業等情形，基於實質課稅原則，將稅捐客體之歸屬完全變更為第三人的情形，其銷售收入及進貨支出應同時一併變更其歸屬，如不承認進項稅額之扣抵，即將產生顯失公平之嚴苛結果的情形。

Value-Added Business Tax, the fulfillment of its tax obligation and its amount, shall be subject to Article 15, Section 1 of the Value-added and Non-value-added Business Tax Act, whereas Article 29 of the Enforcement Rules of the Business Tax Act, stating that input taxes failed to file on time are allowed to postpone its filing, which only serves the purpose of administrative simplicity and the promotion of its efficiency, and shall not,therefore, change the substantial tax law regulations lest it affect the rights or benefits of taxpayers.This Articale holds that calculation of the amount of tax evasion shall return to apply Article 15 of the mother law. On condition that taxpayer failed to submit the evidentiary documents of the amount of input taxes in the current reporting period, supplementary repoting afterwards should still be allowed during tax investigation procedure to ensure the accuracy and objectivity of the amount of tax evasion. No. 660 of J.Y. Interpretation,forbids taxpayers of supplementary repoting afterwards so as to deduct input taxes ,improperly raises the “objective amount of tax payable” and thus only recognize output tax as the amount of tax evasion, namely the calculating basis of punishment, which diverges from the concept of “value added” tax. Such Interpretation is in opposition to the in-dubio-proreo principle in modern constitutional state.It may be suggested that No. 660 of J.Y. Interpretation be understood in a narrower sense before any law amendments added to it. Therefore, to conform to the proportionality principle and ability-to-pay principle in the constitution, deduction of input tax or the approval of estimation on input tax should be allowed especially in the following types:Loss of account books and vouchers due to non-attributive reasons or;Serious unfairness leading to serious damage on condition of the estimation of input tax is not approved.In the case of conducting business without a business registration therefore acquiring input documentary evidences without legal basis as well as in the case of borrowing license practices, for example, activities such as changing the attributees of tax burden completely to third parties, according to the principle of substantial taxation, its sales income along with purchase expenses shall both be attributed together. Otherwise, failure in recognition of the deduction of input tax may worsen the seriousness of unfair taxation.