Cost of Debt
Executive Summary
Key Takeaways
- ✓ Cost of debt is the effective interest rate a company pays on its borrowings.
- ✓ In a WACC build, cost of debt is applied on an after-tax basis to reflect the tax deductibility of interest.
- ✓ After-tax cost of debt = pre-tax cost of debt × (1 − tax rate).
- ✓ Marginal cost of debt (the rate on new borrowing today) differs from embedded cost of debt (the weighted average rate on existing debt), and the correct choice depends on the analytical purpose.
- ✓ Cost of debt is normally lower than cost of equity, since debt holders have priority claim on cash flows and assets.
Definition¶
Cost of debt is the effective interest rate a company pays on its borrowings, reflecting its credit risk and the terms available in current debt markets. In a WACC build, it is one of the two blended components, alongside cost of equity.
After-Tax Adjustment¶
Interest expense is tax-deductible in most jurisdictions, which reduces the company's actual tax bill and therefore the true economic cost of borrowing. WACC applies cost of debt on an after-tax basis to reflect this tax shield:
After-Tax Cost of Debt = Pre-Tax Cost of Debt × (1 - Tax Rate)
Tax deductibility of interest varies by jurisdiction and is subject to limitation rules (such as interest deduction caps) in many tax systems. Practitioners should confirm the applicable rules for the specific jurisdiction rather than assume full deductibility.
Marginal vs. Embedded Cost of Debt¶
Marginal cost of debt is the rate at which the company could raise new debt today, reflecting current market conditions, credit spreads, and the company's present creditworthiness. This is generally the correct input for a forward-looking WACC used in a DCF valuation, since the valuation is concerned with the cost of capital going forward.
Embedded cost of debt is the weighted average rate on debt already outstanding, which may have been raised at different times under different market conditions. Embedded cost of debt reflects historical financing decisions rather than current market terms and is less appropriate as a forward-looking discount rate input, though it may be relevant for other analytical purposes (such as assessing historical financing efficiency).
Estimating Cost of Debt¶
- From actual recent borrowing, if the company has recently raised debt at terms representative of current market conditions
- From comparable corporate bond yields, matched to the company's credit rating and the relevant tenor
- From a synthetic credit rating, where the company's likely rating is estimated from its financial metrics (interest coverage, leverage ratios) and mapped to a corresponding credit spread over the risk-free rate
Where a company carries multiple debt tranches at different rates, a weighted average cost of debt (weighted by each tranche's proportion of total debt) should be calculated before applying the after-tax adjustment.
Audit Considerations¶
- Confirm whether marginal or embedded cost of debt was used, and that the choice matches the analytical purpose (forward-looking valuation should generally use marginal)
- Confirm the tax rate applied for the after-tax adjustment matches the rate used elsewhere in the model and reflects the applicable jurisdiction, including any interest deductibility limitations
- Where multiple debt tranches exist, confirm the weighted average calculation correctly reflects each tranche's proportion
- Confirm cost of debt is lower than cost of equity as a basic sanity check
Common Errors¶
| Error | Description | Risk |
|---|---|---|
| Using pre-tax cost of debt in WACC | Tax shield adjustment omitted | WACC overstated, understating enterprise value |
| Embedded rate used for a forward valuation | Historical average rate applied instead of current market rate | Discount rate does not reflect current cost of capital |
| Inconsistent tax rate | Tax rate in the cost of debt adjustment differs from the rate used elsewhere in the model | Internally inconsistent WACC build |
Continue Reading¶
Prerequisites¶
- Discounted Cash Flow (DCF) Valuation — the parent pillar
Related Glossary¶
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Frequently Asked Questions
Why is cost of debt applied after tax in WACC?
Because interest expense is tax-deductible in most jurisdictions, reducing the company's actual tax bill. The after-tax adjustment, multiplying pre-tax cost of debt by (1 − tax rate), reflects this tax shield so that WACC represents the true net cost of capital to the company.
What is the difference between marginal and embedded cost of debt?
Marginal cost of debt is the rate at which the company could raise new debt today, reflecting current market conditions and credit spreads. Embedded cost of debt is the weighted average rate on debt already outstanding, which may have been issued at different times and rates. Marginal cost of debt is generally the correct input for a forward-looking WACC used in valuation.
How is cost of debt estimated for a private company?
From the company's actual borrowing rate if recently raised and representative of current market terms, or from the yield on comparable-rated corporate bonds or the credit spread implied by the company's credit rating (actual or synthetic) added to the risk-free rate.
Does cost of debt vary if a company has multiple debt tranches at different rates?
Yes. Where a company has multiple classes of debt at different rates, a weighted average cost of debt should be calculated across all tranches, weighted by their relative size, before applying the tax adjustment.
Related Articles
WACC (Weighted Average Cost of Capital)
WACC (Weighted Average Cost of Capital) is the rate of return that a company must earn on its existing assets to maintain the value of its equity and satisfy both its debt holders and equity investors. It is calculated as the weighted average of the after-tax cost of debt and the cost of equity, with the weights determined by the proportion of each in the total capital structure. WACC is used primarily as the discount rate in a discounted cash flow (DCF) valuation, where it converts projected free cash flows into present value. It is also used as a return hurdle: a project or investment is value-creating if its expected return exceeds the WACC.
Cost of Equity
Cost of equity is the rate of return equity investors require to compensate them for the risk of holding a company's stock, given its systematic risk relative to the broader market. It is most commonly estimated using the Capital Asset Pricing Model (CAPM), which expresses cost of equity as the risk-free rate plus a beta-adjusted equity risk premium. Cost of equity serves two roles in a DCF valuation: it is one of the two components blended into WACC (alongside the after-tax cost of debt), and it is used as the sole discount rate when valuing a levered cash flow (FCFE) directly.
Discounted Cash Flow (DCF) Valuation
Discounted cash flow (DCF) valuation values a business, project, or asset as the present value of the cash flows it is expected to generate in the future. It is the most theoretically grounded of the major valuation methodologies, resting directly on the principle that a dollar of cash flow is worth more today than the same dollar received in the future, and that value is created when future cash flows exceed what capital providers require as compensation for the time value of money and risk. This page is the hub for the Knowledge Centre's DCF content: what DCF is and why it works, how free cash flow and discount rates are built, how terminal value is calculated and stress-tested, the method variants practitioners choose between, and — distinctively — how DCF failure modes map onto FMAE's existing structural audit rule taxonomy, since no generic valuation resource ties DCF mechanics to a named, testable audit standard.