When the regulation regarding the maximum debt in the form of the DER ratio has not been issued for tax purposes, the DGT has the authority to determine the maximum debt based on fairness when a loan from a related party. The determination of the DGT can get a rebuttal from the taxpayer because there are corrections that are detrimental to the taxpa yer. This dispute is contained in the Tax Court Decision and is discussed in this article. This article explains that the DGT considers that not all interest expenses from affiliates can be deducted from taxable income. Interest expense that can be deducted is calculated using the DER ratio. Determination of the fairness of the value of the DER ratio and interest rate in calculating interest expense based on TP Doc data submitted by the taxpayer. In the tax year audited, 2015, the taxpayer reported a negative equity value . When calculating a fair DER value, the DGT determines a positive equity value (Rp.28,320,906,207). There is no information on calculating the change in the value of this equity in this Court Decision. The loans are from affiliates not from shareholders. The DGT explained that the interest expense was corrected as a dividend. This result creates a new tax on dividends, but by definition this income is not a dividend. Further studies on this type of income are needed so that it is easier and more definite to follow up.