10.3: Weighted Average Cost of Capital (WACC)

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The weighted average cost of capital (WACC) is the firm’s blended cost of financing—its overall required return from investors. Each financing source (debt, preferred, equity) has a cost and a market weight:

\[ \text{WACC}=w_D\,k_D(1-T_c)+w_P\,k_P+w_E\,k_E \]

where

$w_D,w_P,w_E$ = market-value weights of debt, preferred, and equity,
$k_D,k_P,k_E$ = their respective component costs, and
$T_c$ = corporate tax rate.

Tip: WACC is a benchmark for average-risk projects that resemble the firm’s existing operations. It is not a universal discount rate for every project. If a project is substantially riskier (or safer) than the firm’s typical business, the discount rate should be adjusted.

Conceptually, WACC represents the minimum acceptable return that a firm must earn on its average-risk investments in order to satisfy its investors and maintain firm value. Because WACC is based on market values and required returns, it is inherently forward-looking. It reflects what investors demand today for providing capital, given the firm’s current risk profile, rather than what the firm has paid historically.

Importantly, WACC is not a precisely observable number. Each of its components—capital structure weights and required returns—must be estimated using market data and reasonable assumptions. Small changes in these inputs can materially affect WACC and, in turn, project valuations. As a result, WACC should be viewed as a disciplined estimate grounded in financial theory and market evidence, not a mechanical calculation that produces a single “correct” answer.

10.3.1 Computing WACC Step by Step

Find each component’s market value (see Section 10.1).
Determine the component costs (see Section 10.2).
Compute weights $w_i=V_i/\text{Total Value}$.
Substitute into the WACC formula.

Common Pitfall:

Using book values instead of market values for capital structure weights.
Forgetting to apply the tax adjustment to the cost of debt.
Mixing nominal and effective rates inconsistently across components (APR vs. effective annual).
Using WACC for projects with substantially different risk than the firm’s core business.

Example 10.3A — Computing WACC for Alpha Co.

From Section 10.1: $w_D=0.02,\;w_P=0.03,\;w_E=0.95.$ From Section 10.2: $k_D=6.83\%,\;T_c=25\%,\;k_P=8.0\%,\;k_E=11.2\%.$

\[ \begin{aligned} \text{WACC} &=0.02(0.0683)(1-0.25)+0.03(0.08)+0.95(0.112)\\ &=0.00102+0.00240+0.10640=\mathbf{0.1098}=10.98\%. \end{aligned} \]

Interpretation: Alpha’s average project must earn at least about 11% to meet investor expectations and maintain firm value.

10.3.2 Using WACC for Project Evaluation (Review of Chapter 9)

Net Present Value (NPV) of a project is computed using WACC as the discount rate for average-risk projects:

\[ NPV=\sum_{t=1}^{N}\frac{FCF_t}{(1+\text{WACC})^t}-\text{Initial Investment}. \]

Example 10.3B — BA II Plus NPV with WACC

Project cash flows: $C_0=-500,\;C_1=150,\;C_2=220,\;C_3=260,\;C_4=200.$ WACC = 11% → discount rate = 11.

CF → C0=-500 ENTER
↓ C01=150 ENTER ↓ F01=1 ENTER
Repeat for remaining cash flows.
NPV → I=11 ENTER → ↓ CPT NPV → display ≈ NPV = 135.6.

Interpretation: NPV ≈ $135.6 > 0 ⇒ Accept the project—it earns more than the 11% required return.

10.3.3 Marginal WACC and Project Risk Adjustment

Marginal WACC: the cost of the next dollar of new capital. If issuing new equity or new bonds increases financing costs, the firm’s WACC rises.
Project-specific risk adjustment: use a higher discount rate for riskier projects and a lower discount rate for safer projects. A common classroom approach is to adjust WACC by a few percentage points, but the key idea is matching the discount rate to the project’s risk.

Practice Set G — Computing WACC (Visible Answers)

Debt = $40 M, Equity = $60 M, $k_D=6\%, T_c=24\%, k_E=10\%.$ Compute WACC.
Add preferred stock $10 M ($k_P=8\%$). Re-compute WACC.

Answer Key (Set G)

1. $w_D=0.40,\;w_E=0.60.$ $\text{WACC}=0.4(0.06)(1-0.24)+0.6(0.10)=0.01824+0.06=\mathbf{7.82\%}.$
2. Totals = 40 + 60 + 10 = 110. $w_D=0.364,\;w_P=0.091,\;w_E=0.545.$ $\text{WACC}=0.364(0.06)(0.76)+0.091(0.08)+0.545(0.10)=0.0166+0.0073+0.0545=\mathbf{7.84\%}.$

Practice Set H — Interpreting WACC Changes (Visible Answers)

If interest rates rise from 6% to 9%, how does WACC change if the firm relies heavily on debt?
If tax rates fall from 25% to 15%, what happens to the after-tax cost of debt and overall WACC?
If a firm issues new equity at a higher required return, what happens to WACC?

Answer Key (Set H)

1. Higher rates → higher $k_D$ → WACC rises (significantly if debt-heavy capital structure).
2. Lower tax rate reduces the interest tax shield → after-tax $k_D$ increases → WACC rises slightly.
3. Raising equity with a higher $k_E$ raises WACC since equity’s weight and cost both increase.

Practice Set I — Project Evaluation (Visible Answers)

A firm’s WACC = 9%. Two projects each require $500 investment:

Project A: FCFs = 150, 180, 190, 210, 240
Project B: FCFs = 100, 160, 220, 280, 340

Question: Compute NPV for each using WACC = 9%. Which project should the firm accept?

Answer Key (Set I)

Project A: $NPV \approx \mathbf{\$240.6}$.
Project B: $NPV \approx \mathbf{\$315.6}$.
Decision: Accept Project B (higher NPV).

Key Interpretations & Managerial Implications

Use market-value weights for accuracy.
Use after-tax $k_D$ because interest is generally tax-deductible.
WACC is a hurdle rate for average-risk projects—adjust discount rates for projects with different risk.
If WACC declines, firm value rises (all else equal) because future cash flows are discounted less heavily.
Too much debt can increase financial distress risk and raise $k_E$, which may increase WACC despite the tax shield.

Key Insight: A lower WACC does not automatically mean higher firm value if it is achieved by taking on excessive risk. The goal is not simply to minimize WACC, but to choose a financing mix that supports sustainable value creation while keeping financial distress risk at an acceptable level.

Quick BA II Plus Reference

Store each cash flow with CF keys, then compute NPV using WACC as the discount rate.
Use IRR to compare a project’s internal return to the WACC threshold (accept if IRR > WACC, assuming conventional cash flows and similar risk).

Further Resources

This sets up the leverage–risk trade-offs explored in Section 10.4.

Next → 10.4 Leverage and Risk: We’ll explore how debt magnifies returns and risk through operating and financial leverage, and analyze EPS–EBIT indifference points.

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Example 10.3A — Computing WACC for Alpha Co.

Example 10.3B — BA II Plus NPV with WACC