To calculate the weighted average cost of capital (WACC), you multiply the cost of each funding source, equity and debt, by its proportion of total capital, then add them together. The formula is:
WACC = (E/V × Re) + (D/V × Rd × (1 − Tc))
Where E is the market value of equity, D is the market value of debt, V is E + D (total capital), Re is the cost of equity, Rd is the cost of debt, and Tc is the corporate tax rate. The result tells you the minimum average return a company needs to earn on its assets to satisfy both its shareholders and its lenders.
What Each Variable Means
Before plugging numbers in, it helps to understand what you’re actually measuring with each piece of the formula.
E (market value of equity): For a publicly traded company, this is the share price multiplied by the total number of shares outstanding. It represents what the market thinks the company’s ownership stake is worth today.
D (market value of debt): This includes bonds, loans, and other interest-bearing obligations. Ideally you use the current market value of outstanding bonds, though many analysts use the book value of debt as a practical shortcut since debt market values tend to stay closer to face value than equity does.
V (total capital): Simply E + D. You use V to figure out what percentage of the company’s funding comes from equity and what percentage comes from debt.
Re (cost of equity): The return shareholders expect for investing in the company. This isn’t a number the company sets; it’s derived from a model, most commonly the Capital Asset Pricing Model (CAPM).
Rd (cost of debt): The effective interest rate the company pays on its borrowings.
Tc (corporate tax rate): The company’s effective tax rate. Debt gets a tax adjustment because interest payments are tax-deductible, which makes borrowing cheaper on an after-tax basis.
How to Calculate the Cost of Equity
Most analysts estimate the cost of equity using the Capital Asset Pricing Model:
Cost of Equity = Risk-Free Rate + Beta × (Market Return − Risk-Free Rate)
The risk-free rate is typically the yield on a long-term government Treasury bond, since these are considered virtually default-free. The market return is the expected annual return of the broad stock market. The difference between the market return and the risk-free rate is called the equity risk premium, and it generally falls in the range of 4% to 6% depending on the market and the time period used.
Beta measures how volatile a stock is compared to the overall market. A beta of 1.0 means the stock moves in lockstep with the market. A beta above 1.0 means more volatility (and therefore more risk), which pushes the cost of equity higher. A beta below 1.0 signals lower risk. You can find a company’s beta on most financial data sites.
For example, if the risk-free rate is 4%, the expected market return is 9.5%, and the company’s beta is 1.2, the cost of equity would be: 4% + 1.2 × (9.5% − 4%) = 4% + 6.6% = 10.6%.
How to Calculate the After-Tax Cost of Debt
The cost of debt is simpler to find because it’s based on the interest the company actually pays. One straightforward method: take the total interest expense for the year and divide it by total outstanding debt. That gives you the average interest rate across all borrowings.
You then adjust for the tax benefit. Because companies deduct interest payments as a business expense, borrowing effectively costs less than the stated interest rate. The formula is:
After-Tax Cost of Debt = Rd × (1 − Tc)
If a company pays a 5% interest rate and has a 30% effective tax rate, it saves $1,500 in taxes for every $100,000 in debt. That means it effectively pays only 3.5% on that debt (5% × 0.70). This tax shield is the reason the WACC formula includes the (1 − Tc) term on the debt side but not on the equity side: dividend payments to shareholders are not tax-deductible.
How to Find the Weights
The “weighted” part of WACC comes from calculating how much of the company’s total capital structure is equity and how much is debt. You divide each by V, the total.
Suppose a company has $500,000 in equity and $300,000 in debt. Total capital is $800,000. The equity weight is $500,000 / $800,000 = 0.625, or 62.5%. The debt weight is $300,000 / $800,000 = 0.375, or 37.5%. The two weights always add up to 1.0.
Market value is the standard for these weights rather than book value. Book value reflects what was originally recorded on the balance sheet, while market value reflects what investors would actually pay today. Since WACC is used to evaluate future investment decisions, market-based weights give a more accurate picture of the company’s current cost of capital.
A Full WACC Calculation Example
Let’s walk through the entire formula with a single company. Assume the following:
- Market value of equity (E): $600,000
- Market value of debt (D): $400,000
- Cost of equity (Re): 10%
- Cost of debt (Rd): 5%
- Corporate tax rate (Tc): 25%
First, calculate total capital: V = $600,000 + $400,000 = $1,000,000.
Next, find the weights. Equity weight = $600,000 / $1,000,000 = 0.60. Debt weight = $400,000 / $1,000,000 = 0.40.
Now plug everything in:
WACC = (0.60 × 10%) + (0.40 × 5% × (1 − 0.25))
WACC = 6.0% + (0.40 × 5% × 0.75)
WACC = 6.0% + 1.5%
WACC = 7.5%
This means the company needs to earn at least 7.5% on its investments to meet the combined expectations of its equity investors and debt holders. Any project with an expected return below 7.5% would, in theory, destroy value.
Why WACC Matters
Companies use WACC as the discount rate in discounted cash flow (DCF) analysis, which estimates the present value of future cash flows. A higher WACC means future earnings are worth less today, making a company or project look less valuable. A lower WACC has the opposite effect.
WACC also serves as a hurdle rate for new projects. If a company’s WACC is 7.5%, a proposed expansion that’s only expected to return 5% wouldn’t clear the bar. It would cost more to fund the project than the project would earn.
Investors use WACC to compare companies within the same industry. A firm with a lower WACC has a cheaper cost of capital, which often signals lower perceived risk or a more efficient capital structure. Two companies can have identical revenues and still look very different through the lens of WACC if one carries significantly more debt or has a much higher beta.
What Changes Your WACC
Several factors push WACC up or down. Rising interest rates increase the cost of debt directly and often raise the risk-free rate used in the cost of equity calculation, lifting WACC from both sides. A company that takes on more debt might lower its WACC initially because debt is cheaper than equity (thanks to the tax shield), but at some point additional leverage increases financial risk, which raises both the cost of debt and the beta on its stock.
Industry matters too. Utilities and consumer staples companies tend to have lower betas and steadier cash flows, which translates to lower costs of equity. Technology startups and cyclical businesses typically carry higher betas and therefore higher WACCs. The tax rate plays a role as well: a company with a higher effective tax rate gets a larger tax benefit from its debt, slightly reducing the after-tax cost of borrowing.