The after-tax cost of equity is the same as the pre-tax cost of equity. Unlike interest on corporate debt, dividends paid to shareholders are not tax-deductible, so there is no tax shield to subtract. When you build a weighted average cost of capital, the cost of equity goes in at face value. The tax adjustment applies only to debt.
Why Equity Gets No Tax Shield
A corporation pays income tax on its profits first. Whatever’s left can be distributed to shareholders. The IRS puts it plainly: “The corporation does not get a tax deduction when it distributes dividends to shareholders,” and the profit is “taxed to the corporation when earned, and then is taxed to the shareholders when distributed as dividends.”1Internal Revenue Service. Forming a Corporation That double taxation is the reason the after-tax figure equals the pre-tax figure. There’s nothing to deduct.
Debt works differently. Federal law allows a deduction for “all interest paid or accrued within the taxable year on indebtedness.”2Office of the Law Revision Counsel. 26 USC 163 – Interest A company paying 8% interest on a bond at a 21% corporate tax rate effectively pays about 6.3% after the tax savings (8% × 0.79). Dividends never get that discount. If shareholders require a 10% return, the company’s after-tax cost of that equity stays at 10%.
The federal corporate tax rate sits at a flat 21%, and it remains permanent even after many individual tax provisions expired at the end of 2025. Because dividends were never deductible, no change to the corporate rate has any mathematical effect on the cost of equity. A rate cut lowers the after-tax cost of debt. It does nothing to equity.
How It Enters WACC
Weighted average cost of capital blends the cost of equity and the after-tax cost of debt by their weights in the capital structure. The cost of debt is multiplied by (1 − tax rate). The cost of equity is not.
Take a company financed 60% with equity and 40% with debt, with a 10% cost of equity, a 6% pre-tax cost of debt, and a 21% corporate tax rate:
- Equity component: 60% × 10% = 6.0%
- Debt component: 40% × 6% × (1 − 0.21) = 1.90%
- WACC: 6.0% + 1.90% = 7.90%
Applying a tax adjustment to the equity side as well is one of the more common spreadsheet errors in corporate finance. It understates WACC and can greenlight projects that don’t actually clear the company’s real hurdle rate. Keep the tax factor on the debt line and nowhere else.
Estimating the Cost of Equity
Since there’s no tax adjustment to apply, the whole calculation reduces to estimating the return shareholders require. Two models dominate.
CAPM
The Capital Asset Pricing Model is the standard approach:
Cost of Equity = Risk-Free Rate + Beta × Equity Risk Premium
The risk-free rate is typically the yield on the 10-year U.S. Treasury bond, published daily by the Federal Reserve. At the start of 2026, that yield sat around 4.2%.3Federal Reserve Economic Data. Market Yield on U.S. Treasury Securities at 10-Year Constant Maturity, Quoted on an Investment Basis Beta measures how much a stock moves relative to the overall market: 1.0 tracks the market, below 1.0 is less volatile, above 1.0 more so. The equity risk premium is the extra return investors expect from stocks over the risk-free rate; estimates at the start of 2026 ran roughly 4.2% to 4.5%.
With a 4.2% risk-free rate, a beta of 1.2, and a 4.3% equity risk premium:
Cost of Equity = 4.2% + 1.2 × 4.3% = 9.36%
Because dividends aren’t deductible, 9.36% is both the pre-tax and after-tax figure.
Beta is the only company-specific input, and it moves the answer more than anything else. A utility at beta 0.5 with the same market assumptions comes in at 6.35%. A high-growth tech firm at beta 1.8 lands at 11.94%. Analysts commonly compare beta figures across data providers before settling on one.
Dividend Discount Model
For companies paying steady, growing dividends, the Gordon Growth version of the Dividend Discount Model offers an alternative:
Cost of Equity = (Expected Dividend per Share ÷ Current Stock Price) + Dividend Growth Rate
For a company expected to pay a $3.00 dividend next year, trading at $60, with a 5% historical dividend growth rate:
Cost of Equity = ($3.00 ÷ $60) + 5% = 10%
Same rule: 10% is both pre-tax and after-tax.
The growth rate is the tricky part. One method uses the sustainable growth rate: return on equity multiplied by the retention ratio (the share of earnings not paid out as dividends). A company earning 15% on equity and retaining 60% of profits would have a 9% sustainable growth rate. The inputs come from the annual report or 10-K filing, which contains audited financial statements and dividend history.4Investor.gov. Form 10-K
The DDM assumes dividends grow at a constant rate indefinitely. That’s a reasonable fit for mature, stable payers. For fast-growing firms that reinvest most of their earnings or don’t pay dividends at all, CAPM is the better tool.
Where the Debt Advantage Narrows
The tax shield on debt is real but capped. Federal law limits the deductible amount of business interest expense to 30% of adjusted taxable income, with some additions for business interest income and floor-plan financing.2Office of the Law Revision Counsel. 26 USC 163 – Interest Interest above the cap carries forward but doesn’t reduce taxes in the current year.
A highly leveraged company may not capture the full shield the textbook after-tax debt formula assumes. When part of the interest deduction is disallowed, the effective after-tax cost of debt drifts back toward the pre-tax rate. That narrows the gap between debt and equity, but it doesn’t change the cost of equity itself. Equity remains unaffected because it was never deductible to begin with.
What About Investor Taxes and Buybacks
A few related tax items sit adjacent to the cost of equity without changing how you calculate it.
Most dividends from U.S. corporations qualify for the long-term capital gains rate structure: 0%, 15%, or 20%, depending on the investor’s taxable income.5Office of the Law Revision Counsel. 26 USC 1 – Tax Imposed Higher-income investors also face a 3.8% net investment income tax on dividends and capital gains once modified adjusted gross income crosses $200,000 for single filers or $250,000 for joint filers.6Office of the Law Revision Counsel. 26 USC 1411 – Imposition of Tax These are shareholder-level taxes. They influence the returns investors ultimately keep, but standard cost-of-equity models operate at the corporate level and don’t adjust for them.
Stock buybacks carry a 1% excise tax on the fair market value of shares a publicly traded domestic corporation repurchases during the year, offset by new shares issued in the same year.7Office of the Law Revision Counsel. 26 USC 4501 – Repurchase of Corporate Stock That’s a friction on returning capital through equity channels, not a change to the CAPM or DDM output.
The Practical Rule
Whether you’re running a WACC, building a discounted cash flow model, or setting a hurdle rate for a project, treat the cost of equity as a pre-tax and after-tax figure at the same time. Feed it in as-is. Apply (1 − tax rate) only to debt. That single discipline keeps the model honest and preserves the real reason companies favor debt up to a point: the tax code subsidizes interest and does not subsidize dividends.