Plain definition
Weighted average cost of capital, or WACC, combines the required return on equity with the after-tax cost of debt using their weights in the capital structure. It is commonly used to discount cash flows that have risk similar to the company’s existing operations. The debt component is normally after tax because interest can reduce taxable profit where that tax benefit is available.
WACC is a starting point, not a neutral answer for every project. It can be unsuitable for a project with materially different risk, a different currency, a changing target funding mix, or cash flows that already include financing effects. The inputs need a documented basis; a formula cannot repair inconsistent assumptions.
Illustrative example
Suppose a business is funded 60% by equity requiring 12% and 40% by debt costing 5% after tax. Its WACC is 9.2%: 60% × 12% gives 7.2%, and 40% × 5% gives 2.0%. Finance may use 9.2% as a reference for a project that resembles the existing business.
It should not automatically use 9.2% for a volatile foreign-market launch. Management must decide whether the project’s cash-flow risk and currency require an adjustment or a separate appraisal approach.
| Equity component (60% × 12%) | |
|---|---|
| After-tax debt component (40% × 5%) | |
| WACC |
Use market-based or current decision-relevant weights where practical. Historical book values can describe the past while misrepresenting the funding investors would support today.
Why it matters
A blended rate prevents a team from valuing an equity-funded business at only its borrowing cost or treating equity as free. It also exposes when the investment case relies on a financing assumption that the business cannot sustain.
Practical consequence
Write the equity and debt weights, the return or cost used for each, the tax treatment, date, source, and reason the funding mix is appropriate. Recalculate the components separately before combining them. Then test whether the project’s risk, currency, and financing treatment match the use of WACC; if they do not, state the adjustment rather than hiding it in one rate.