If a Discounted Cash Flow valuation is the engine of corporate finance, WACC is the fuel. The Weighted Average Cost of Capital is the single number that tells you what return a business has to clear, every year, just to be worth what it costs.
It also happens to be the number most analysts get wrong. A 1-point error in WACC can move a valuation by 20% or more — which is why understanding the formula, not just plugging into it, matters.
WACC in One Line
WACC is the blended after-tax return required by all of a company's investors — equity holders and debt holders combined, weighted by their share of the capital structure.
It's the minimum return a project, an acquisition, or the business as a whole must earn to be value-creating. Earn less than WACC and you destroy value, no matter how positive the accounting profit looks.
The WACC Formula, Broken Down
WACC = (E/V × Re) + (D/V × Rd × (1 − T))
Where:
• E = Market value of equity
• D = Market value of debt
• V = E + D (total capital)
• Re = Cost of equity
• Rd = Cost of debt (pre-tax)
• T = Marginal tax rate
Cost of equity component
The return equity investors require to bear the risk of holding the stock. Always higher than cost of debt, because equity is junior in the capital stack — equity holders get paid last and lose first.
Cost of debt component
The pre-tax yield the company pays on its debt. For public companies, this is the yield to maturity on outstanding bonds. For private companies, it's the all-in rate on new debt the company could raise today — not the rate on a 5-year-old loan.
Tax shield adjustment
Interest expense is tax-deductible. So the effective cost of $1 of interest is only (1 − T) × $1. This is why debt is cheaper than equity in WACC math — not just because debt yields less, but because the tax shield reduces the effective cost further.
Finding Cost of Equity Using CAPM
The Capital Asset Pricing Model (CAPM) is the industry-standard way to estimate cost of equity:
Re = Rf + β × (Rm − Rf)
Risk-free rate
Use the yield on the 10-year government bond of the country the company operates in. For US companies, this is the 10-year Treasury — currently around 4.4%. For Eurozone, the 10-year Bund. For Brazil, the 10-year NTN-F. Use the bond that matches your DCF currency and forecast horizon.
Equity risk premium
The extra return investors demand for holding stocks instead of risk-free bonds. The single most widely-cited source is Aswath Damodaran's annual update — typically 4.5–6.0% for developed markets, 7–12% for emerging markets. Pick a value, document the source, defend it.
Beta
A measure of how the stock moves relative to the broader market. β = 1 means the stock moves with the market; β > 1 means more volatile; β < 1 means less volatile.
For public companies, beta is observable on Bloomberg or Yahoo Finance. For private companies, use the industry average beta from comparable public peers, then unlever and relever it to match your company's capital structure:
Unlevered β = Levered β / [1 + (1 − T) × (D/E)]
Take the median unlevered beta of 5–10 public comps, then relever using your target capital structure to get the right β for your DCF.
Finding Cost of Debt
Three approaches, in descending order of preference:
1. Yield to maturity on the company's existing publicly-traded bonds (gold standard).
2. Synthetic credit rating: estimate the company's rating from interest coverage and leverage metrics, then use the spread for that rating + risk-free rate.
3. Effective interest rate (Interest Expense / Average Debt) — quick and dirty, but uses historical rates, not current ones. Avoid unless you have nothing else.
Whatever method you use, the cost of debt should be forward-looking, not historical. A company that locked in 3% debt three years ago can't refinance at 3% today — its true cost of debt is whatever it would pay on new debt now.
Capital Structure: Book vs Market Weights
WACC weights should be based on market values, not book values.
For public companies, equity market value = share price × diluted shares outstanding. For debt, use book value if the company isn't in distress (it's a decent proxy for market value when credit spreads are normal).
For private companies — and for forward-looking DCFs of public companies — use target capital structure, not current snapshot. A startup with 100% equity today won't stay that way; build WACC around where the company will eventually settle, typically the industry median.
5 Mistakes That Break Your WACC
• 1. Using book value of equity. Equity weight should be market cap, not balance-sheet equity. Book value reflects historical contributions; market value reflects current required return.
• 2. Forgetting the tax shield. Cost of debt must be after-tax in the WACC formula. Pre-tax rate inflates WACC by 1–3 points.
• 3. Mixing currencies. Risk-free rate, equity risk premium, and beta should all be in the same currency as your DCF cash flows. A USD DCF discounted at a EUR WACC will produce a number that means nothing.
• 4. Using snapshot capital structure for a long-dated DCF. A 10-year DCF should use target leverage, not today's leverage. Otherwise WACC drifts as the company organically changes capital structure.
• 5. Using levered beta directly from a peer. Two companies in the same industry can have very different betas if they have different leverage. Always unlever to industry average, then relever to your company's target structure.
WACC for Private Companies (the Tricky Part)
Public-company WACC has observable inputs: market cap, share price, traded bond yields, comparable betas. Private companies have none of these.
The standard workaround:
4. Pick 5–10 public comparable companies (same sector, similar size, similar business model).
5. Pull their levered betas; unlever each using their actual leverage.
6. Take the median unlevered beta — this is your industry beta.
7. Relever using your target capital structure → your levered beta.
8. Plug into CAPM with current risk-free rate and ERP → your cost of equity.
Many practitioners then add an additional size premium (typically 100–300 bp for small-cap or micro-cap companies, per the Duff & Phelps annual report) to reflect the illiquidity and small-firm risk that beta alone doesn't capture.
Result: most private-company WACCs land in the 11–18% range, materially higher than the 8–12% you'd see for mid-cap public companies. That's the cost of being private and small.
|
Stop second-guessing your WACC Our WACC Calculator Template pulls each input through CAPM, handles unlevering and relevering of beta, applies the tax shield correctly, and builds a sensitivity table on capital structure. Plug your comps in and get an audit-ready WACC in 10 minutes. → Download the WACC Calculator → |
FAQ
Why is WACC higher than the cost of debt?
Because WACC also includes the cost of equity, which is always higher than debt. Equity holders take more risk (last to be paid, first to lose) and demand a higher return.
Should WACC change over time in my DCF?
In theory, yes — if capital structure changes materially during the forecast period. In practice, most analysts use a single WACC throughout, assuming the company will converge to target leverage. Multi-period WACC adds complexity that rarely changes the answer by more than a percent or two.
What's a reasonable WACC for a typical company?
Large-cap S&P 500 companies: 7–10%. Mid-cap: 9–12%. Small-cap public: 11–14%. Private SMBs: 13–18%. Early-stage growth companies: 15–25%. Higher WACC ≠ worse company — it just reflects higher risk and the need for stronger cash flows to justify investment.
Can I just use an industry-average WACC?
For a quick screen, yes. For a serious valuation, no. Two companies in the same industry can have very different optimal capital structures, growth profiles, and risk levels. Industry averages are a starting point, not a destination.