Weighted average cost of capital (WACC)
The weighted average cost of capital is the blended cost of equity and debt, weighted by their proportion in the capital structure. It is the discount rate used in DCF because it represents the average return required by all investors (equity and debt holders) in the company.
The name is somewhat confusing: WACC is not the cost to the company; it is the required return to its investors. But it is called "cost of capital" because from the company's perspective, the return shareholders and bondholders demand is the cost of raising capital.
Quick definition
WACC is the weighted average of the cost of equity and the after-tax cost of debt:
WACC = (E/V × Re) + (D/V × Rd × (1 - T))
Where:
E = Market value of equity
D = Market value of debt
V = E + D (total firm value)
Re = Cost of equity
Rd = Cost of debt (before tax)
T = Corporate tax rate
(1 - T) = Tax adjustment factor
Key takeaways
- WACC is a blended cost because companies raise capital from both equity (stocks) and debt (bonds/loans).
- Equity holders are riskier (they are last in line if the company fails), so they demand higher returns. Debt holders are safer, so they accept lower returns.
- WACC is "weighted" by the market value of equity and debt, not book value. Use current stock price and current bond prices or yields, not balance sheet values.
- The cost of debt is multiplied by (1 - Tax rate) because interest is tax-deductible. If a company pays 5% interest and the tax rate is 21%, the after-tax cost is 5% × (1 - 0.21) = 3.95%.
- A typical mature US company might have WACC of 7–9%. A high-leverage company might be 8–10%+. A low-leverage utility might be 5–6%.
- WACC is the discount rate used in DCF. It represents the return you demand to invest in the company given its risks and capital structure.
The three building blocks: E, D, and V
To calculate WACC, you need three things:
1. Market value of equity (E)
This is the company's market capitalization: current stock price × number of shares outstanding.
Example: Apple has ~16.3 billion shares outstanding and trades at ~$200 per share. Market cap (E) = $3.26 trillion.
Do not use book value of equity (from the balance sheet). Use market value. If the stock price changes, E changes, and so does WACC.
2. Market value of debt (D)
This is the total amount of borrowed money the company owes. You can estimate it by:
- Direct approach: Look at the balance sheet. Sum all debt: short-term debt, long-term debt, lease obligations (under IFRS), etc. This is an estimate of fair value assuming the company's credit spread has not changed since issuance.
- Market approach (more precise): If the company has publicly traded bonds, use their current market price. Large companies' bonds trade, and their market value reflects current credit risk.
Example: Apple has ~$107 billion in total debt (short-term + long-term).
3. Total value (V)
V = E + D. For Apple: V = $3.26 trillion + $0.107 trillion = $3.367 trillion.
Calculating the weights
The weights are simply the proportion of equity and debt in the capital structure:
- Weight of equity: E/V
- Weight of debt: D/V
For Apple:
- Weight of equity: $3.26T / $3.367T = 96.8%
- Weight of debt: $0.107T / $3.367T = 3.2%
This means WACC will be dominated by the cost of equity (96.8% weight) with a small contribution from the after-tax cost of debt (3.2% weight).
Calculating cost of equity (Re)
The cost of equity is the return shareholders demand, given the company's risk. It is typically estimated using the Capital Asset Pricing Model (CAPM):
Re = Rf + β × (Rm - Rf)
Where:
Rf = Risk-free rate (typically 10-year Treasury yield)
β = Beta (systematic risk relative to the market)
Rm - Rf = Market risk premium (typical range 5–6%)
We will cover CAPM in detail in the next article, but for now: If the risk-free rate is 4%, beta is 1.1, and market risk premium is 5.5%, then:
Re = 4% + 1.1 × 5.5% = 4% + 6.05% = 10.05%
Calculating cost of debt (Rd)
The cost of debt is the interest rate the company pays on borrowed money. You can find it by:
-
Looking at the interest expense on the income statement — Divide total interest expense by total debt to get the weighted average cost of debt.
Example: If a company paid $500 million in interest expense on $10 billion in debt, the cost is 500/10,000 = 5%.
-
Looking at the company's credit rating and market spreads — If the company has an A-rated bond yielding 4.5% and the risk-free rate is 4%, the cost is 4.5%.
-
Using the company's own bond yields — If the company has publicly traded bonds, their current yield is the current cost of debt.
Example: Apple's cost of debt is roughly 4.5% (the weighted average of its various bond issuances).
The tax adjustment: why (1 - T)?
Interest expense is tax-deductible. If a company pays $100 million in interest and has a 21% tax rate, it reduces taxable income by $100 million, saving $21 million in taxes. So the true after-tax cost is not 5%, but 5% × (1 - 0.21) = 3.95%.
This is why debt is cheaper than equity: the government subsidizes it through the tax deduction.
Rd × (1 - T) = After-tax cost of debt
For Apple: 4.5% × (1 - 0.21) = 4.5% × 0.79 = 3.555%
Putting it together: a full WACC calculation
Example: Microsoft (as of mid-2026)
Market data (approximate):
- Stock price: $415
- Shares outstanding: 2.6 billion
- Market cap (E): $415 × 2.6B = $1.079 trillion
- Total debt (D): $65 billion (from balance sheet)
- Total value (V): $1.079T + $0.065T = $1.144 trillion
- 10-year Treasury yield (risk-free rate): 4.0%
- Microsoft beta: 0.95 (less volatile than market)
- Market risk premium: 5.5%
- Cost of debt (Rd): 3.2% (Microsoft's bonds yield about 3.2%)
- Tax rate (T): 13% (effective tax rate)
Step 1: Calculate weights
- E/V = 1.079 / 1.144 = 94.3%
- D/V = 0.065 / 1.144 = 5.7%
Step 2: Calculate cost of equity
- Re = 4.0% + 0.95 × 5.5% = 4.0% + 5.225% = 9.225%
Step 3: Calculate after-tax cost of debt
- Rd × (1 - T) = 3.2% × (1 - 0.13) = 3.2% × 0.87 = 2.784%
Step 4: Calculate WACC
- WACC = 0.943 × 9.225% + 0.057 × 2.784%
- WACC = 8.699% + 0.159% = 8.86%
This is Microsoft's discount rate. All future cash flows from Microsoft would be discounted at 8.86% to calculate present value.
Sensitivity of WACC to inputs
Small changes in cost of equity or cost of debt can shift WACC. Let us sensitivity-test Microsoft:
If cost of equity is 8.5% instead of 9.225%:
- WACC = 0.943 × 8.5% + 0.057 × 2.784% = 8.013% + 0.159% = 8.17%
- Change: -0.69 percentage points
If cost of debt is 4.2% instead of 3.2% (market stress, yields rise):
- After-tax: 4.2% × 0.87 = 3.654%
- WACC = 0.943 × 9.225% + 0.057 × 3.654% = 8.699% + 0.208% = 8.91%
- Change: +0.05 percentage points (small, because debt is only 5.7% of capital)
The cost of equity dominates the WACC calculation for companies that are mostly equity-financed. If a company were 50% debt-financed, changes in cost of debt would matter more.
Real examples of WACC across industries
Utility (Duke Energy, low risk):
- Mostly debt-financed (high leverage)
- Cost of equity: ~7.5%
- Cost of debt: ~2.5% (investment-grade)
- WACC: ~4.5–5.5% (low because of high leverage and low cost of debt)
Consumer staples (Procter & Gamble, moderate risk):
- Balanced capital structure
- Cost of equity: ~8.5%
- Cost of debt: ~3.5%
- WACC: ~6.5–7.5%
Large-cap tech (Microsoft, lower risk for its category):
- Mostly equity-financed (low leverage)
- Cost of equity: ~9%
- Cost of debt: ~3%
- WACC: ~8.5–9%
Growth tech or biotech (riskier):
- Mostly equity-financed
- Cost of equity: ~14–18%
- Cost of debt: ~5–7% (if any debt; often none)
- WACC: ~14–18%
Notice: companies with higher risk (biotech) have higher WACC. Companies with higher leverage (utilities) can have lower WACC despite similar business risk, because debt is cheaper and they use it heavily.
Common mistakes in WACC calculation
Mistake 1: Using book value of equity instead of market value
Wrong: "The company has $5 billion in equity on the balance sheet, so E = $5 billion."
Right: Use market cap. "The company has 1 billion shares at $25 per share, so E = $25 billion."
Book value is historical; market value is current. Market value is what matters for WACC.
Mistake 2: Using a fixed WACC for all years
This is usually fine for simplicity, but if the company's leverage changes significantly, WACC changes. A startup that becomes profitable and raises debt will see its WACC rise (cost of equity may fall due to lower risk, but the debt weight increases). Project this if material.
Mistake 3: Forgetting the tax adjustment on debt
Wrong: "The cost of debt is 5%, so I use 5% in WACC."
Right: "The cost of debt is 5%, so the after-tax cost is 5% × (1 - 0.21) = 3.95%, and I use that."
This mistake overstates the cost of capital, understating DCF value.
Mistake 4: Using the wrong risk-free rate
Different maturities have different yields. The 2-year Treasury might yield 3.8%, the 10-year 4.2%, the 30-year 4.4%. For a company whose cash flows are spread over 10+ years, the 10-year Treasury is the most appropriate risk-free rate. For very long-duration companies (utilities), some analysts use the 20-year or 30-year yield.
Mistake 5: Mixing market value and book value
Wrong: "E is $25 billion (market cap) and D is $5 billion (book value from the balance sheet), so V = $30 billion."
Right: If you use market value of E, use market value of D too (current bond prices, not book value). If market values are unavailable, use book value for both, but note the caveat.
WACC for different capital structures
A company that is mostly debt-financed (like a utility: 50% debt, 50% equity) has a lower WACC than a company that is mostly equity-financed (like a tech startup: 5% debt, 95% equity), assuming the same business risk.
Why? Because debt is cheaper than equity (interest is tax-deductible, and debt holders demand lower returns for lower risk). So by using more debt, a utility lowers its overall cost of capital.
But there is a limit. As leverage increases, default risk increases, and the cost of debt (and cost of equity) both rise to compensate. At some point, the benefit of cheap debt is offset by the risk premium required. Most companies find their optimal capital structure (lowest WACC) at 30–50% debt for stable, profitable businesses.
FAQ
Q: What if a company has no debt?
A: Then D = 0, D/V = 0, and WACC = Re (the cost of equity). Many startups and young growth companies are all-equity financed. Their WACC is just the return shareholders demand, with no contribution from debt.
Q: What if a company has preferred stock?
A: Include it. Preferred stock is a hybrid between debt and equity. It usually has a fixed dividend (like a bond's coupon) and a specific cost of capital. Some analysts treat it as part of debt; others as a separate weight. Check the company's balance sheet and capital structure documentation.
Q: Should I use marginal tax rate or effective tax rate?
A: Theoretically, marginal (the tax rate on the next dollar of income). Practically, use the effective tax rate (total tax paid / pretax income from the income statement) or the statutory rate (21% federal in the US, plus state taxes). The difference is usually small.
Q: How often should I recalculate WACC?
A: When material variables change: cost of equity (if risk-free rate or market risk premium changes), cost of debt (if credit spreads widen), or capital structure (if the company raises new debt or equity). For a multi-year DCF, recalculating WACC annually is often overkill. Recalculate if you see a major change in market conditions.
Q: What if the company is in a different country?
A: Use the country's risk-free rate (10-year sovereign yield), and adjust the market risk premium for country risk. An emerging-market company might have a market risk premium of 8–10% instead of the US 5.5% to reflect currency and political risk. Or add a country risk premium separately. This is beyond the scope of this beginner article, but it is important for international valuations.
Related concepts
- Cost of equity — The return shareholders demand, estimated via CAPM.
- Cost of debt — The interest rate paid on borrowed money.
- Capital structure — The mix of equity and debt; affects WACC weighting.
- Tax shield — The value of the tax deduction on interest; makes debt cheaper after-tax.
- Market value vs book value — Always use market values for WACC weights, not book values.
Summary
WACC is simply a weighted average of the returns demanded by equity holders (higher risk, higher return) and debt holders (lower risk, lower return). The formula is straightforward, but the inputs (cost of equity, cost of debt, capital structure) must be calculated carefully using market values, not book values.
The most common mistakes are using book values instead of market values, forgetting the tax adjustment, and anchoring WACC to a "standard" percentage instead of calculating it specifically for the company. By building a clean WACC calculation and sensitivity-testing it, you can avoid most errors.
In the next article, we will dive into cost of equity and the CAPM—the model that estimates how much return shareholders demand, and how to estimate it from observable market data.
Next
Authority: CFA Institute (WACC calculation), US Federal Reserve (risk-free rates), SEC (financial statement analysis for debt valuation).