Cost of debt and debt valuation

..just as a piece of revision .is my understanding correct Mv of debt is always present value of future cash flows at required investor rate of return If redeemable we do like irr way ..with taking into consideration the tax allowance for interest But for redeemable cost of debt we do irr without taking into account the tax allowed for interest that would investor rate of return and cost of debt to company we incorporate tax allowed for interest to reach the figure by way of irr calculation . For iredemable cost of debt it's either Kd= interest (1-t)/ market value Or Kd(1-t) Where kd is investor rate of return And mv of iredemable debt ...it's interest / kd Is there anything I m wrong or missing .please guide Thank u