Cost of Debt: The Effective Borrowing Rate a Company Pays to Lenders

Corporate Finance

Understand cost of debt, how it is estimated, and why the after-tax cost matters in WACC and valuation.

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The cost of debt is the effective rate a company pays to borrow money. It represents the return lenders require for extending credit to the business.

In practice, the cost of debt depends on the firm’s credit risk, interest-rate environment, collateral, covenant strength, and debt maturity.

Why Cost of Debt Matters

Cost of debt matters because it feeds into:

Weighted Average Cost of Capital (WACC)
firm valuation
financing decisions
capital structure planning

A lower borrowing cost can help reduce the firm’s overall capital cost, but only if leverage remains sustainable.

Basic Idea

If a company can issue debt at 7%, then 7% is a reasonable starting point for its pre-tax cost of debt.

For WACC purposes, analysts often use the after-tax cost of debt:

$$ R_d(1-T) $$

Where:

\(R_d\) is pre-tax borrowing cost
\(T\) is the tax rate

This reflects the tax shield created when interest expense is deductible.

Why Debt Is Usually Cheaper Than Equity

Debt is often cheaper than equity because lenders have:

contractual payments
higher claim priority
sometimes collateral support

That said, debt is not free. If leverage rises too far, lenders demand more compensation and the cost of debt can climb sharply.

Example

Suppose a company can borrow at 6% and faces a 25% tax rate.

Then the after-tax cost of debt is:

6\%(1-0.25)=4.5\%

That 4.5% is the debt component typically used in WACC.

What Raises Cost of Debt

Cost of debt tends to rise when:

credit quality weakens
leverage increases
interest rates rise
business cash flows become more volatile

A risky company may face much higher debt cost than a stable, investment-grade borrower.

Weighted Average Cost of Capital (WACC): Uses after-tax cost of debt as one of its components.
Cost of Capital: The broader financing benchmark for the firm.
Cost of Equity: The return required by shareholders rather than lenders.
Tax Shield: Explains why after-tax debt cost is often lower than pre-tax borrowing cost.
Interest Rate: A key market input affecting debt pricing.

FAQs

Should cost of debt use coupon rate or market yield?

In valuation, market yield is often more relevant because it reflects the current opportunity cost of borrowing.

Why is after-tax cost of debt used in WACC?

Because interest is often tax deductible, reducing the effective economic cost of borrowing.

Can too much debt raise the overall cost of capital?

Yes. Excess leverage can raise both debt and equity risk, pushing up the firm’s total capital cost.

Revised on Monday, May 18, 2026

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