Article — WACC Calculator (Weighted Avg Cost of Capital)
WACC Calculator: the Discount Rate for Firm Valuation
WACC is the Weighted Average Cost of Capital, the average rate of return a firm pays its capital providers, weighted by the share of each type of capital. The standard formula is WACC = (E/V) · Re + (D/V) · Rd · (1 - Tc), where E and D are market values of equity and debt, V is their sum, Re is the cost of equity (typically from CAPM), Rd is the pre-tax cost of debt, and Tc is the corporate tax rate. WACC is the discount rate used in DCF firm valuation and the hurdle rate for capital budgeting decisions.
The WACC calculator above takes the five inputs and returns the weighted rate, plus capital-structure weights and after-tax cost of debt as intermediate values. The formula is unambiguous; the work is in measuring the inputs. CFA Institute curriculum, McKinsey Valuation, and Damodaran corporate-finance texts use the same form.
What WACC measures
WACC is a blended cost of capital. Equity investors and debt holders both fund the firm; both expect a return. The firm's funding cost is the average of these two, weighted by how much it has of each. Once you account for tax-deductibility of interest, the after-tax WACC drops below the pre-tax blended rate.
The number has three uses. As a discount rate for DCF firm valuation. As a hurdle rate for capital budgeting: only projects with expected returns above WACC create shareholder value. As an EVA benchmark setting the threshold for value creation.
The Miller-Modigliani propositions (1958, 1963) provide the theoretical foundation for WACC. The 1958 paper showed that, in a frictionless world, the value of a firm is independent of its capital structure — WACC is constant. The 1963 paper added the tax-deductibility of interest, creating the tax shield that makes leveraged firms slightly more valuable. The (1 - Tc) factor in the modern WACC formula traces directly to this 1963 addition.
The WACC formula, term by term
The formula has three terms: the equity weight times cost of equity, plus the debt weight times the after-tax cost of debt. Weights are E/V and D/V, where V = E + D. Cost of equity Re uses CAPM. Cost of debt Rd is the pre-tax yield. Tax rate Tc is the marginal corporate rate (21% federal in the US since 2017; add state taxes if material).
Worked example. A firm has 600 million USD equity and 400 million USD debt, so V = 1,000 million. Cost of equity is 10%; cost of debt is 5% pre-tax; tax rate is 21%. After-tax cost of debt is 5% × (1 - 0.21) = 3.95%. WACC = (0.60 × 10%) + (0.40 × 3.95%) = 6.00% + 1.58% = 7.58%. The calculator above runs this in one keystroke and shows each weight, cost component, and contribution.
Rf = 4.40% (10-yr Treasury, Fed H.15)ERP = 5.5% (Damodaran 2024)Tc (US fed) = 21% (IRC §11)Beta source = Bloomberg, Yahoo, regressionRd source = bond YTM, bank facility rateCost of equity via CAPM
Cost of equity is the harder input. The standard approach is the Capital Asset Pricing Model: Re = Rf + beta · (Rm - Rf). Risk-free rate (Rf) is the 10-year US Treasury yield, currently around 4.4% per Federal Reserve H.15. Beta measures the firm's equity sensitivity to market returns; published betas are available from Bloomberg, Yahoo Finance, and Damodaran's NYU Stern dataset. The equity risk premium (Rm - Rf) is the expected excess return of the market over the risk-free rate; the long-run US historical average is about 5.5% (Damodaran 2024 forward estimate).
For a firm with beta 1.2, Re = 4.4% + 1.2 · 5.5% = 11.0%. Industry averages run from about 8% for utilities (beta 0.65) to 12% for tech (beta 1.30). Levered beta should match the firm's capital structure; comparable-firm betas usually need an unlever-relever step.
Past stock returns are not a forward-looking cost of capital. Earnings yield (E/P), book ROE, and historical share-price CAGR all measure different things. CAPM with current Rf and a defensible ERP is the standard. Multi-factor models (Fama-French 3F or 5F) are alternatives in academic work; for practical valuation, CAPM remains the workhorse.
Cost of debt and the tax shield
Cost of debt is easier. For a firm with publicly traded bonds, Rd is the yield to maturity on the firm's outstanding bonds. For a firm with bank loans only, the all-in rate on its credit facility is acceptable. For a firm with mixed funding, take a weighted average of the various debt instruments at their market values.
The tax shield matters. Interest payments are tax-deductible (IRC Section 163), so each dollar of pre-tax interest costs only (1 - Tc) after tax. At 21% federal tax, a 6% pre-tax debt yield costs the firm 4.74%. This is why debt looks cheaper than equity. Section 163(j) caps deductibility for some firms; adjust if the limit binds.
WACC and the optimal capital structure
The WACC formula shows debt as cheaper than equity, suggesting more debt always reduces WACC. In practice, beyond some level, increasing debt raises both Re and Rd because the firm becomes riskier. The trade-off creates an inverted-U shape: WACC falls at low leverage as the tax shield expands, then rises as financial-distress costs and risk-adjusted Re overwhelm the shield.
Industry-typical leverage ratios vary widely. Damodaran's 2024 industry data shows banks at 85% debt, utilities at 50%, automakers at 40%, retail at 30%, software at 5%. Comparable-firm WACC for a target valuation should match the target's steady-state capital structure, not necessarily its current one.
For private-firm valuation where market value of equity is not observable, iterate: assume a capital structure, compute WACC, discount cash flows to get firm value, derive implied equity value, check against assumed weight, repeat. Two or three iterations usually converge.
WACC in DCF valuation
DCF firm valuation uses WACC as the discount rate for forecast unlevered free cash flows. Sum the PV of explicit-period FCFs plus a terminal value, both at WACC, for enterprise value. Subtract net debt to get equity value. Standard in sell-side research, M&A advisory, and IFRS goodwill impairment testing.
WACC sensitivity matters. A 100 basis point change can shift firm value by 15 to 25 percent depending on growth assumptions. SEC-required goodwill impairment disclosures (ASC 350) report WACC and terminal growth used, because both drive the impairment conclusion.
- Typical large-cap US WACC = 7-10%
- Utility WACC = 5-7% (low beta, high D/V)
- Tech / software WACC = 10-12% (high beta, low debt)
- Bank WACC = 4-6% (regulatory debt levels)
- US federal Tc = 21% (post-TCJA 2017)
- Damodaran ERP = ~5.5% (current US)
Common WACC mistakes
Three errors recur in practice. Using book values instead of market values for the weights — the most common WACC mistake. Book equity is historical sunk cost; market cap reflects current expectations. Always use market values unless the firm is unlisted and equity must be implied.
Using the effective tax rate instead of the marginal rate. Effective rate (cash taxes ÷ pre-tax income) reflects timing differences and credits. The marginal rate is what matters for the tax shield on incremental debt. US firms paying full federal corporate tax use 21%; add state corporate tax for the combined rate.
Mixing nominal cash flows with a real discount rate. WACC should be nominal if cash flows are nominal (the usual case); for real cash flows, subtract expected inflation from each WACC component. Mismatching produces wrong present values.