Glossary term
Cost of Debt
Cost of debt is the effective rate a borrower pays to use borrowed money, usually measured before or after the tax benefit of deductible interest.
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What Is Cost of Debt?
Cost of debt is the effective rate a company, household, or project pays to use borrowed money. In corporate finance, it usually refers to the interest rate a business pays on loans, bonds, notes, or other interest-bearing obligations.
The concept matters because debt is not free capital. Even when debt helps fund growth, acquisitions, working capital, or real estate, the borrower must earn enough return to cover interest, principal repayment, fees, refinancing risk, and any constraints in the loan documents.
Key Takeaways
- Cost of debt measures the financing cost of borrowed money.
- It can be measured before tax or after tax when interest is deductible.
- The rate depends on credit risk, collateral, maturity, market rates, covenants, and borrower leverage.
- Companies use cost of debt in capital budgeting, WACC, valuation, and leverage decisions.
- A low coupon is not the whole cost if fees, floating rates, refinancing risk, or restrictive terms are important.
Cost of Debt Formula
A common after-tax version is:
The interest rate is the borrowing cost before tax. The tax rate reflects the tax benefit of deductible interest. If a company pays 8% interest and has a 25% tax rate, the after-tax cost of debt is 6% because interest deductibility reduces the net cost.
That simple formula is most useful for plain debt with deductible interest. Analysts may use yield to maturity for traded bonds, a weighted average rate across all borrowings, or a market-based estimate for new debt.
Pre-Tax Versus After-Tax Cost
Measure | What it shows | Common use |
|---|---|---|
Pre-tax cost of debt | Financing cost before tax effects | Loan pricing, interest burden, credit comparison |
After-tax cost of debt | Borrowing cost after interest tax shield | WACC, capital budgeting, valuation |
The after-tax version is common in corporate finance because interest expense can reduce taxable income. The pre-tax version still matters because cash interest has to be paid on schedule. A tax benefit does not eliminate liquidity risk.
How Companies Use It
Cost of debt is one input in the weighted average cost of capital, or WACC. A company comparing a new factory, acquisition, buyback, or refinancing asks whether the expected return is high enough to justify the capital used. Debt may be cheaper than equity, but too much debt can raise risk and eventually make all capital more expensive.
Credit analysts also watch cost of debt because it can signal changing market confidence. If a company must refinance at a much higher rate, free cash flow can fall even if revenue has not changed.
What Changes the Cost
Market rates set the backdrop, but borrower-specific risk drives the spread. Stronger borrowers with stable cash flows, valuable collateral, conservative leverage, and good access to capital usually borrow more cheaply. Weaker borrowers pay more or may lose access entirely.
Loan structure also matters. Floating-rate debt can become more expensive when benchmark rates rise. Short maturities can create refinancing pressure. Covenants can protect lenders but limit borrower flexibility. Fees, discounts, and call protection can change the true economic cost.
Where It Can Mislead
Cost of debt is not the same as interest expense. Interest expense is a dollar amount over a period. Cost of debt is a rate. It is also not the same as default risk, although the two are related. A borrower can have a low historical cost of debt and still face higher future borrowing costs if credit conditions change.
For investors and business owners, the practical question is whether the debt-funded activity earns more than the real cost of financing after considering taxes, risk, and cash timing.
The Bottom Line
Cost of debt is the effective rate paid to use borrowed money. It helps connect financing choices to valuation, cash flow, and risk, but it should be read with maturity, fees, tax treatment, covenants, and refinancing conditions.