Cost of debt

Kd is never used as a discount factor. Kd is the return to investors and is therefore always before tax. When using the cost of debt in the calculation of the WACC then we always need the after-tax cost of debt. As to how we calculate it depends on whether the debt is redeemable or irredeemable. All of this is explained in my free lectures, and I am not going to type out my lectures here!