Lesson Overview
Capital budgeting tools like NPV and IRR only work if the discount rate is chosen correctly. That discount rate comes from the firm’s cost of capital: the return investors require to provide funding.
In this lesson, you will learn what the cost of capital represents, how firms estimate it using the weighted average cost of capital (WACC), and why risk is the central driver of required returns.
Learning Objectives
- Explain what the cost of capital represents.
- Define WACC and describe its components.
- Distinguish between the cost of debt and the cost of equity.
- Understand why equity is typically more expensive than debt.
- Explain how capital structure affects WACC.
- Recognize common mistakes when applying WACC in practice.
What Is the Cost of Capital?
The cost of capital is the minimum return a project must earn to compensate investors for the time value of money and the risk they bear.
From the firm’s perspective, it is a cost because failing to meet this return makes investors worse off. From the investor’s perspective, it is a required return.
A useful intuition:
- If a project earns more than the cost of capital, it creates value.
- If a project earns less than the cost of capital, it destroys value.
Why Risk Drives Required Return
Investors demand higher returns for taking on more risk. A stable utility business can raise capital cheaply, while a speculative startup must offer much higher expected returns.
The cost of capital increases when:
- Cash flows are more volatile or uncertain.
- Revenues depend heavily on economic cycles.
- Operating leverage or financial leverage is high.
- Information about the business is limited or unclear.
Debt vs Equity: Different Claims, Different Costs
Cost of Debt
Debt holders receive fixed payments and have priority over equity holders if the firm runs into trouble. Because debt is less risky, investors accept a lower required return.
Interest on debt is also tax-deductible in many jurisdictions, which reduces its effective after-tax cost to the firm.
Cost of Equity
Equity holders are residual claimants. They are paid only after all obligations are met and absorb the bulk of business risk.
Because equity is riskier, its required return is higher than the cost of debt.
The Weighted Average Cost of Capital (WACC)
Most firms finance operations using a mix of debt and equity. The weighted average cost of capital combines the required returns of each source, weighted by their share of total financing.
At a high level, WACC reflects the average return required by all capital providers.
Conceptually, WACC answers this question:
If the firm undertakes an average-risk project, what return must it earn to satisfy all investors?
Why WACC Is Used as a Discount Rate
When a project has risk similar to the firm’s existing operations, WACC is an appropriate discount rate for NPV analysis.
Using WACC ensures that:
- Projects earning more than WACC increase firm value.
- Projects earning less than WACC reduce firm value.
- Investment decisions remain consistent with financing expectations.
Capital Structure and WACC
Capital structure refers to the mix of debt and equity a firm uses. Changing this mix changes WACC, but not always in obvious ways.
- Adding debt can lower WACC because debt is cheaper and offers tax benefits.
- Too much debt increases financial distress risk.
- As risk rises, both the cost of debt and cost of equity increase.
The result is a tradeoff: moderate leverage may reduce WACC, but excessive leverage raises it.
Project Risk vs Firm Risk
A common mistake is applying the same WACC to every project. WACC reflects the firm’s average risk, not the risk of every possible investment.
Examples:
- A regulated utility launching a stable infrastructure upgrade may use firm WACC.
- The same utility entering a volatile new market should use a higher discount rate.
Matching the discount rate to project risk is critical for good capital allocation.
Hurdle Rates in Practice
Many firms use hurdle rates that exceed their estimated WACC. Reasons include:
- Forecasting uncertainty and optimism bias.
- Capital rationing and limited managerial capacity.
- Strategic or regulatory constraints.
While conservative hurdle rates can prevent bad investments, overly high rates can also cause firms to pass on value-creating projects.
Mini Example: Why Cost of Capital Matters
Suppose a firm has a WACC of 9 percent. It considers a project expected to earn a 7 percent return.
- The project is profitable in accounting terms.
- It still destroys value because it fails to meet investor expectations.
Without the cost of capital as a benchmark, this distinction would be easy to miss.
Common Mistakes to Avoid
- Using a single WACC for projects with very different risk profiles.
- Ignoring taxes when estimating the cost of debt.
- Confusing historical returns with required returns.
- Treating WACC as a fixed number instead of a moving estimate.
- Adjusting cash flows and discount rates for the same risk twice.
Key Terms
- Cost of capital The required return demanded by investors.
- WACC Weighted average cost of capital across debt and equity.
- Cost of debt Required return to lenders, adjusted for taxes.
- Cost of equity Required return to shareholders.
- Capital structure The mix of debt and equity financing.
- Hurdle rate Minimum acceptable return for an investment.
Practice: Check Your Understanding
- Why is the cost of capital described as a required return?
- Why is equity typically more expensive than debt?
- When is WACC an appropriate discount rate?
- How can too much debt increase WACC?
- What is one risk of using an overly high hurdle rate?
What’s Next?
In Lesson 4.5: Debt vs Equity and Capital Structure, we’ll go deeper into financing choices, leverage, and the tradeoffs between risk, return, and control.