Weighted Average Cost of Capital: Formula, Inputs, and Example

The weighted average cost of capital formula is WACC = (E/V × Re) + (D/V × Rd × (1 − T)), with a third term, P/V × Rp, added when a company has preferred stock outstanding. It blends what a company pays for each source of financing, weighted by how much of each source sits in the capital structure, and expresses the result as a single percentage. That percentage is the minimum return the business must earn on its assets to satisfy both lenders and shareholders.

What Each Symbol Means

Before plugging in numbers, pin down what the letters stand for:

  • E is the market value of equity.
  • D is the market value of debt.
  • P, when used, is the market value of preferred stock.
  • V is total capital: E + D (+ P if preferred stock exists).
  • Re is the cost of equity.
  • Rd is the pre-tax cost of debt.
  • Rp is the cost of preferred stock.
  • T is the corporate tax rate.

The equity piece, E/V × Re, is equity’s share of capital times what shareholders expect to earn. The debt piece, D/V × Rd × (1 − T), is debt’s share times the interest rate, reduced by the tax benefit of deducting interest. Add the pieces and you have WACC. The rest of the work is finding honest numbers for each input.

Calculating the Cost of Equity

The standard approach is the Capital Asset Pricing Model: Cost of Equity = Risk-Free Rate + Beta × Equity Risk Premium. Three inputs, each with its own quirks.

The risk-free rate comes from U.S. Treasury bond yields, usually the 10-year note. Because the federal government backs those bonds, the yield represents a return available without corporate default risk. Treasury yields move daily, so pull a current number rather than a historical average.

Beta measures how a stock moves relative to the market overall. A beta of 1.0 tracks the market. Above 1.0 means more volatility; below 1.0 means less. A utility might sit near 0.5; a high-growth tech firm might land at 1.5 or higher. Financial data providers publish beta estimates built from historical price movements, and different providers can give different numbers for the same company.

The equity risk premium is the extra return investors demand for holding stocks instead of risk-free Treasuries. Estimates typically run from about 4% to 7% depending on methodology and market conditions. Aswath Damodaran at NYU Stern publishes regularly updated implied premium estimates that many practitioners reference. Picking the high end versus the low end can swing cost of equity by several percentage points, so the choice matters.

Calculating the Cost of Debt

Cost of debt starts with something observable: the interest rate the company actually pays. For publicly traded bonds, use the yield to maturity. For bank loans, use the stated rate. If a company carries multiple instruments at different rates, take a weighted average across them.

Then apply the tax adjustment. Interest on business debt is generally deductible from taxable income, so the government effectively absorbs part of the cost.1Office of the Law Revision Counsel. 26 USC 163 – Interest Multiply the pre-tax rate by (1 − T). A company paying 6% interest at a 21% tax rate has an after-tax cost of debt of roughly 4.74%.

The federal corporate income tax rate is a flat 21% of taxable income.2Office of the Law Revision Counsel. 26 USC 11 – Tax Imposed Most companies also owe state corporate income tax, which runs from roughly 2% to 11.5% depending on the state. Analysts typically use a blended effective rate that combines federal and state obligations rather than the federal rate alone.

The Section 163(j) Cap

The tax shield on debt is not unlimited. For most businesses, deductible business interest expense in a given year is capped at business interest income plus 30% of adjusted taxable income.3Internal Revenue Service. Questions and Answers About the Limitation on the Deduction for Business Interest Expense Interest above the cap carries forward rather than disappearing.

A small business exemption applies to companies with average annual gross receipts of $25 million or less (adjusted for inflation) over the prior three years. Those businesses deduct all their interest without hitting the cap.3Internal Revenue Service. Questions and Answers About the Limitation on the Deduction for Business Interest Expense

Starting in tax years after 2025, the calculation tightens. Adjusted taxable income will no longer allow companies to add back depreciation and amortization, shifting the base from an EBITDA-like measure to an EBIT-like one. Capital-intensive businesses with heavy depreciation will be able to deduct less interest, which pushes up their effective after-tax cost of debt.

Adding Preferred Stock

Preferred stock sits between debt and common equity in the capital structure. Preferred shareholders receive a fixed dividend, much like a bond coupon, but the payment is a dividend rather than interest. That distinction matters for taxes: preferred dividends are generally not deductible from the issuing company’s taxable income. A narrow exception exists for certain public utility companies with preferred stock issued before October 1, 1942, which is irrelevant for virtually every modern corporation.4eCFR. 26 CFR 1.247-1 – Deduction for Dividends Paid on Preferred Stock of Public Utilities

Because there is no tax shield, the cost of preferred stock has no (1 − T) adjustment. The formula is simply Cost of Preferred Stock = Annual Dividend / Current Market Price per Share. A preferred share trading at $100 that pays $6 per year has a cost of 6%. When a company issues new preferred shares, flotation costs reduce the net proceeds and push the effective cost slightly higher.

Weighting Each Component

Once you have each cost, you need each proportion. The weight for a component equals its market value divided by total market value of all capital. For equity, multiply the current stock price by shares outstanding. For debt, ideally use the market value of outstanding bonds and loans; in practice, book value is a reasonable stand-in for companies that are not in financial distress, because debt market and book values stay close when a company is healthy.

Market values matter more than book values because book values reflect what investors paid historically, not what the capital is worth today. A company whose stock has tripled since its IPO would badly understate equity’s share of the mix using book value. Weights need to reflect current economic reality, and they must add up to 100%.

For companies whose capital structure is in motion, say after a major acquisition or a planned debt paydown, some analysts use a target capital structure rather than the current snapshot. The logic is that WACC should reflect where the company is headed, not a temporary state.

A Worked Example

Take a company with $600 million in equity market value, $400 million in debt, no preferred stock, a cost of equity of 10%, a pre-tax cost of debt of 5%, and a 25% blended tax rate. Step by step:

  • Total capital (V): $600M + $400M = $1 billion
  • Equity weight (E/V): $600M / $1B = 0.60
  • Debt weight (D/V): $400M / $1B = 0.40
  • Weighted cost of equity: 0.60 × 10% = 6.00%
  • After-tax cost of debt: 5% × (1 − 0.25) = 3.75%
  • Weighted cost of debt: 0.40 × 3.75% = 1.50%
  • WACC: 6.00% + 1.50% = 7.50%

Notice how much the equity side dominates. Even though equity’s rate is only twice the after-tax debt rate, it contributes four times as much to WACC because equity makes up a larger share of the base.

Where To Find the Inputs

Publicly traded companies disclose most of what you need. The annual Form 10-K filed with the SEC carries audited financial statements, outstanding debt balances, and interest expense.5Legal Information Institute. Form 10-K Share prices and shares outstanding come from any financial data provider or stock exchange. Beta estimates are published by Bloomberg, Reuters, and free sources like Yahoo Finance.

Pull the risk-free rate as a current Treasury yield from the U.S. Treasury’s website or any bond data platform. The equity risk premium is the most subjective input; analysts either use a long-run historical average of stock returns over Treasury returns or an implied forward-looking estimate derived from current market prices. For the tax rate, use the company’s actual effective rate, which combines the 21% federal rate with applicable state taxes.2Office of the Law Revision Counsel. 26 USC 11 – Tax Imposed

Limitations Worth Knowing

WACC is the standard tool for discounting cash flows, but it rests on assumptions that do not always hold. Where it breaks down matters as much as how to calculate it.

  • Constant capital structure. The formula assumes debt-to-equity stays steady over time. Companies pay down debt, issue shares, or lever up for acquisitions, so a single WACC applied to a ten-year cash flow stream quietly assumes periodic rebalancing that rarely happens.
  • Single risk profile. A firm-wide WACC applies one beta to the whole company. A conglomerate with a media division and a theme-park division faces different economic forces in each, and using the company-wide rate for both leads to over-investing in the riskier business and under-investing in the safer one. The fix is a divisional cost of capital built from comparable “pure play” companies, with their betas unlevered and relevered to the target’s debt-to-equity ratio.
  • Subjective inputs. Beta varies by data provider and lookback period. Reasonable equity risk premium estimates span several percentage points. The risk-free rate depends on the maturity you pick. Small changes compound into meaningfully different WACC figures.
  • Private companies. Without a public stock price, there is no observable market capitalization or trading beta. Analysts estimate both from comparable public companies and apply adjustments for illiquidity and size, adding more judgment.
  • Tax rate uncertainty. The debt tax shield assumes the company has enough taxable income to use the deduction. Firms with net operating losses or those hitting the Section 163(j) cap get less benefit from debt than the formula implies.3Internal Revenue Service. Questions and Answers About the Limitation on the Deduction for Business Interest Expense

None of this makes WACC useless. It makes it a starting point that requires judgment. Experienced analysts treat the output as a range rather than a precise figure and test how sensitive their valuations are to different assumptions about capital costs. That sensitivity work is usually where the real insight lives.