# WACC: Estimating a Company's Weighted Average Cost of Capital

Calculate WACC with market-value weights, after-tax debt cost, and a defensible equity return, then match it correctly to unlevered cash flow.

Canonical: https://wiki.fcontext.com/stocks/wacc/
Fact checked: 2026-07-22

> For educational purposes only; not investment advice.

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## Direct answer

**Weighted average cost of capital (WACC)** is an estimate of the return required by all long-term capital providers, weighted by the market value of equity and interest-bearing debt. In a standard enterprise DCF, it discounts unlevered free cash flow because that cash flow is available before payments to either group.

`WACC = E/(D+E) × Re + D/(D+E) × Rd × (1−T)`

Here, `E` and `D` are market values, `Re` is the cost of equity, `Rd` is the current pre-tax cost of debt, and `T` is the marginal tax rate applicable to deductible interest. WACC is an assumption, not an observable fact or the company's historical return.

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## How the estimate works

Use market-value weights because valuation asks what capital costs now. Equity is usually diluted shares times current price. Debt should include interest-bearing borrowings at market value when obtainable; book value may be a disclosed approximation when debt trades near par. Treat leases, preferred stock, excess cash, pensions, and minority interests consistently with the cash-flow and enterprise-value definitions.

The cost of equity is often estimated with CAPM: `Re = risk-free rate + beta × equity risk premium`. Every input is contestable: maturity and currency of the risk-free rate, beta window and leverage, and equity-premium method. Academic evidence shows that industry equity-cost estimates can be imprecise, so false decimal precision is especially misleading.

The cost of debt is the yield the company would pay on comparable borrowing today, not the coupon on old debt. The factor `(1−T)` reflects the value of tax-deductible interest, but only to the extent the company can use deductions and local rules permit them. Losses, interest limitations, changing jurisdictions, or financial distress can reduce the effective shield.

Match numerator and denominator. Discount unlevered cash flow in the same currency and nominal or real terms with WACC. Discount cash flow to equity with cost of equity instead. A constant WACC assumes capital structure and business risk converge toward the modeled target; major leverage changes require explicit treatment or an adjusted-present-value approach.

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## Worked calculation and DCF sensitivity

Suppose a company has $6 billion of equity and $4 billion of debt. Its estimated cost of equity is 10%, current pre-tax debt cost is 6%, and marginal tax rate is 25%:

- Equity weight: `$6bn / $10bn = 60%`
- Debt weight: `$4bn / $10bn = 40%`
- After-tax debt cost: `6% × (1−25%) = 4.5%`
- WACC: `60% × 10% + 40% × 4.5% = 7.8%`

If next year's unlevered free cash flow is $500 million and is assumed to grow perpetually at 3%, a simplified terminal value is `$500m / (7.8%−3%) = $10.42bn`. At 8.8% WACC it falls to `$500m / (8.8%−3%) = $8.62bn`, about 17.2% lower. This is not a price target: it isolates how a one-point discount-rate change affects a long-duration estimate.

A useful model presents a WACC/growth sensitivity table, reconciles debt and cash to the latest 10-K, and explains why beta, premium, tax, and target leverage were chosen. Reverse the process as well: calculate what WACC or growth the current market value appears to imply.

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## Risk and research checklist

- Use a valuation date and market values from that date; do not mix a current share price with stale debt or share counts.
- Reconcile debt, leases, cash, diluted shares, and noncontrolling interests to filings and notes.
- Match currency, inflation basis, duration, and country risk between cash flow and discount rate.
- Normalize beta for unusual leverage or short trading history; compare a peer-based relevered beta.
- Estimate the marginal borrowing rate from current yields or credit spreads, not average interest expense alone.
- Test whether tax deductions are usable and whether interest caps change the effective rate.
- Model target rather than accidental capital structure when current leverage is temporary.
- Use ranges for WACC and terminal growth; keep terminal growth below WACC and economically defensible.
- Do not apply one corporate WACC to divisions with materially different business or country risk.
- Stress refinancing, recession, downgrade, dilution, and distress scenarios; leverage can make both component costs rise together.

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## Common misconceptions

- “WACC is the interest rate.” Debt is only one component; equity normally has no contractual rate but still has an opportunity cost.
- “More cheap debt always lowers WACC.” Higher leverage eventually raises default risk and the required returns on both debt and equity.
- “Book-value weights are more objective.” They are accounting measures and may not represent current capital-provider claims.
- “The tax shield always equals the statutory tax rate.” Deductibility and the ability to use deductions determine its value.
- “A company's WACC is a precise published number.” It changes with markets and depends on estimation choices.
- “WACC discounts every cash flow.” It fits unlevered enterprise cash flow; equity cash flow requires an equity discount rate.
- “A one-point change is minor.” Terminal values can be highly sensitive when WACC is close to perpetual growth.

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## Related topics

- [Discounted Cash Flow](/stocks/discounted-cash-flow/)
- [Capital Asset Pricing Model](/stocks/capm/)
- [Enterprise Value](/stocks/enterprise-value/)

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## Authoritative sources

- [The Cost of Capital, Corporation Finance and the Theory of Investment](https://www.jstor.org/stable/1809766) - Franco Modigliani and Merton H. Miller, *American Economic Review*
- [Corporate Income Taxes and the Cost of Capital: A Correction](https://www.jstor.org/stable/1809167) - Franco Modigliani and Merton H. Miller, *American Economic Review*
- [Industry Costs of Equity](https://doi.org/10.1016/S0304-405X(96)00896-3) - Eugene F. Fama and Kenneth R. French, *Journal of Financial Economics*
- [How to Read a 10-K](https://www.sec.gov/answers/reada10k.htm) - U.S. Securities and Exchange Commission