The weighted average cost of capital (WACC) is the single most important rate in corporate finance. It is the discount rate inside a discounted-cash-flow valuation, the hurdle rate a CFO uses to decide whether to build a new factory, and the bar a leveraged buyout has to clear to make money for its sponsors. Get WACC wrong by a percentage point and your valuation moves by tens of percent. Get it wrong by two and a deal that looked accretive becomes value-destructive.
TL;DR: WACC is the blended cost of every dollar a company has raised – equity plus debt – weighted by how much of each it uses. The formula is simple. The inputs are not. Cost of equity comes from the capital asset pricing model. Cost of debt comes from the company’s bond yield, tax-adjusted. The weights come from market values, not book. Use book weights, lever the wrong beta, or forget the tax shield and the number is meaningless.
The formula, in one place
WACC = (E / V) × Re + (D / V) × Rd × (1 – T)
- E = market value of equity (share price × diluted shares outstanding)
- D = market value of debt (bond prices, or book value when bonds don’t trade)
- V = E + D (total capital)
- Re = cost of equity, almost always estimated with CAPM
- Rd = pre-tax cost of debt (yield to maturity on outstanding bonds)
- T = marginal effective tax rate
The CFA Institute’s cost-of-capital refresher presents the same formula and is the standard reference for the inputs. The expression generalizes to any number of capital sources – preferred stock, hybrid securities, multiple debt tranches – by adding a weighted term for each.
Cost of equity: where CAPM enters
The cost of equity is what shareholders demand in expected return for bearing equity risk. The capital asset pricing model estimates it as:
Re = Rf + β × (Rm – Rf)
Where Rf is the risk-free rate (10-year US Treasury yield is the standard proxy), β is the stock’s sensitivity to the market, and (Rm – Rf) is the equity risk premium. As of June 17, 2026, the 10-year Treasury constant maturity rate is 4.49% per the Federal Reserve H.15 release. The equity risk premium is harder. Aswath Damodaran’s implied equity risk premium series is the most widely cited source; long-run historical estimates cluster around 4.5%-5.5%.
Cost of debt: bond yields, not coupons
The pre-tax cost of debt is the yield to maturity an investor would earn buying the company’s outstanding bonds today – not the coupon rate the company is paying. If a company issued a 5% coupon bond five years ago and that bond now trades at a yield of 6%, the cost of debt for valuation purposes is 6%. The tax adjustment multiplies by (1 – T) because interest payments are tax-deductible in the US, creating an interest tax shield. For most large US corporations the marginal rate to use is 21% federal plus a couple of points of state tax, so around 23%-25%.
A worked example with realistic numbers
Take a hypothetical large-cap industrial, Acme Manufacturing, with the following capital structure:
| Input | Value | Where it comes from |
|---|---|---|
| Share price | $120 | Quote |
| Diluted shares outstanding | 500 million | 10-Q cover page |
| Market value of equity (E) | $60,000 million | 120 × 500m |
| Market value of debt (D) | $20,000 million | Bond pricing service |
| Total capital (V) | $80,000 million | E + D |
| Equity weight (E/V) | 75.0% | |
| Debt weight (D/V) | 25.0% | |
| Risk-free rate (10y UST) | 4.49% | Fed H.15, 6/17/2026 |
| Beta | 1.10 | 5y monthly regression vs S&P 500 |
| Equity risk premium | 5.00% | Damodaran implied ERP |
| Cost of equity (Re) | 9.99% | 4.49% + 1.10 × 5.00% |
| Pre-tax cost of debt | 5.50% | YTM on outstanding bonds |
| Tax rate | 24.0% | Effective marginal rate |
| After-tax cost of debt | 4.18% | 5.50% × (1 – 0.24) |
Plugging into the WACC formula:
WACC = 0.75 × 9.99% + 0.25 × 4.18% = 7.49% + 1.04% = 8.54%
Acme’s hurdle rate is 8.54%. Any new project the company funds with this mix of equity and debt has to earn more than that to create value. Any DCF on Acme should discount free cash flow at 8.54%.
How WACC varies across industries
Sector WACCs are not all the same. Stable, regulated, debt-heavy industries like utilities run low single-digit WACCs because lenders charge them little and equity holders accept modest returns for the predictability. High-beta, equity-heavy tech sectors run double-digit WACCs because the cash flows are riskier and there is less tax-deductible debt in the mix. Below is a snapshot from Damodaran’s US industry dataset.
| Sector | Cost of equity | After-tax cost of debt | D / (D+E) | WACC |
|---|---|---|---|---|
| Software (Internet) | 11.48% | 3.97% | 10.95% | 10.66% |
| Semiconductor | 10.72% | 3.97% | 2.53% | 10.55% |
| Semiconductor Equipment | 10.18% | 3.97% | 4.64% | 9.89% |
| Retail (Building Supply) | 10.80% | 3.97% | 18.89% | 9.51% |
| Software (System & App) | 9.64% | 3.97% | 5.28% | 9.34% |
| Power | 6.10% | 3.55% | 42.58% | 5.01% |
| Banks (Regional) | 5.73% | 3.55% | 34.25% | 4.98% |
| Utility (General) | 5.02% | 3.55% | 44.90% | 4.36% |
Where WACC goes wrong
The formula is a one-liner. The mistakes are not. The five that show up most often in DCF audits:
1. Book weights instead of market weights
The textbook is explicit: use market values. A company with $30 billion in book equity and a $200 billion market cap is mostly equity-funded, and the equity weight in WACC should reflect that. Using book value inflates the debt weight, understates WACC, and produces inflated DCF valuations. This is the single most common error.
2. Using the coupon rate as cost of debt
A 10-year bond issued at a 3% coupon in 2020 may now yield 6% in the secondary market. The cost of debt is the current market yield, not what the company is paying on legacy paper. If the company had to refinance today, it would refinance at the market yield.
3. Ignoring the tax shield – or applying the wrong rate
Interest is deductible, dividends are not. That asymmetry is exactly why WACC has a (1 – T) term on the debt side. The right T is the marginal effective rate, not the historical reported effective rate, which can be distorted by one-time items.
4. Using the wrong beta
For a private company or a project inside a diversified parent, the right beta is the industry beta – the unlevered (asset) beta of comparable public peers, re-levered to the target company’s own debt-to-equity ratio. Using the parent’s reported beta or a peer’s levered beta directly is wrong if capital structures differ.
5. Forgetting that WACC changes
A company that levers up post-LBO has a different WACC than the same company pre-LBO. Rising risk-free rates push WACC up across the board. Sector beta drifts. A WACC computed five years ago is stale – rebuild it before you use it.
How WACC fits into the bigger picture
WACC is the discount rate inside every discounted cash flow valuation. It is the hurdle rate corporate-development teams use when comparing M&A targets. It is the rate that private-equity sponsors have to beat when structuring a leveraged buyout. It anchors decisions about whether to issue equity, raise debt, or buy back stock. It is one input in choosing between projects via NPV and IRR.
The intellectual debt is to the Modigliani-Miller capital structure theorems, which formalized why the mix of debt and equity matters for a company’s cost of capital in a world with taxes. The CFA Institute curriculum and Damodaran’s cost-of-capital research remain the most accessible reference points for practitioners.
Sources
- CFA Institute – Cost of Capital: Foundational Topics
- Aswath Damodaran – WACC by US Sector dataset
- Aswath Damodaran – Implied Equity Risk Premium series
- Federal Reserve – H.15 Selected Interest Rates
- SEC Office of Investor Education – Discounted Cash Flow basics
Disclosure: This article was produced with AI assistance and reviewed before publication. It is for informational purposes only and is not investment advice.