WACC calculator
Estimate the firm-level weighted average cost of capital: combine equity and debt weights (by market value) with cost of equity, pre-tax cost of debt, and a marginal tax rate for the interest deduction. Output includes weights, after-tax debt cost, and WACC as a percentage.
Use the marginal rate relevant to interest tax shield (not effective book rate unless that is your assumption).
Formula in plain terms
WACC = (E / V) × Re + (D / V) × Rd × (1 − T), where V = E + D. Equity cost is not tax-adjusted in this standard form; debt is reduced by the corporate tax shield on interest.
After this, run NPV
When the discount rate matches your WACC story, open the NPV calculator and paste your judgment on the project cash flows. If risk differs materially from the whole company, consider a project-specific rate instead of raw WACC.
Frequently asked questions
Market vs book weights?
Use market values for typical valuation WACC.
Pre-tax Rd?
Yes—tax is applied inside the formula on the debt leg.
Use with NPV?
Often yes as a starting discount rate when assumptions align.