- The cost of debt measures the current cost of the firm of borrowing funds to finance its assets
- It should be a function of the default risk that lenders perceive in the firm
- The default risk of a firm is a function of two variables:
- The firm's capacity to generate cash flows from operations; also, the volatility in these cash flows
- The extent of its financial obligations (interest and principal payments)
- The most widely used measure of a firm's default risk is its bond rating assigned by the independent ratings agency
- We can estimate the cost of debt by using their ratings and associated default spreads
- The long term bonds outstanding of the company that are widely traded can be used to estimate the cost of debt
- The market price of the bond can serve to compute a yield we can use as the cost of debt
Synthetic rating
- Also applicable for unrated, smaller and private firms
- Play the role of a rating agency and assign a rating to a firm based on its Interest Coverage ratio.


- Interest is tax deductible and the resulting tax savings reduce the cost of borrowing to firms
After-tax cost of debt = Pretax cost of debt * (1 - Marginal tax rate)
- To obtain the tax advantages of borrowing, firms have to be profitable; there is no tax advantages from interest expenses to a firm that has operating losses
After-tax cost of debt = Pretax cost of debt if operating income < 0
Pretax cost of debt * (1 - t) if operating income > 0