What is Cost of Debt?

The cost of debt is the effective interest rate that an enterprise pays on all sources of debt, including loans, bond issues, lines of credit, and other debt securities, as a percentage. It shows how costly the financing of the enterprise through debt rather than equity is, and it serves as one of the main elements used in financial analysis, such as the calculation of WACC.

Cost of Debt Formula

The basic cost of debt equation for calculating the pre-tax cost of debt is:

For the after-tax cost of debt, the formula is:

The after-tax calculation considers the tax savings from interest expenses to determine the effective borrowing cost. 

Here is an example for cost of debt calculation:

• Interest expense: $50,000
• Total debt: $1,000,000

Using the debt cost formula:

Cost of Debt = ($50,000 ÷ $1,000,000) × 100 = 5%

The company’s pre-tax cost of debt is therefore 5%.

If its applicable tax rate is 25%:

After-Tax Cost of Debt = 5% × (1 − 25%) = 3.75%

This means the company’s effective borrowing cost after the tax benefit is 3.75%.

Why the Cost of Debt Is Important?

• Indicator of financial strength: When the cost of debt increases, it signals that credit risk has become higher and/or that credit conditions have tightened; when the cost of debt is low and stable, it may signify healthy creditworthiness
• Benchmarking: By comparing cost of debt against other companies in the same industry, it can be seen whether the terms of borrowing of the company under analysis are favorable
• Capital structure decision-making: In combination with the cost of equity, cost of debt is taken into consideration for determining the optimal balance between debt and equity capital structures
• Feeds into WACC: Cost of debt affects the calculation of the WACC (along with the cost of equity)

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