WACC analysis: interpret the cost of funding a business

WACC analysis explains how a business's debt cost, equity cost, and funding mix combine into its weighted average cost of capital. It starts with supplied finance assumptions, not an interest expense total. A useful review shows the contribution of each funding source and the checks behind the combined rate.

What WACC measures

Debt providers require compensation for lending, and equity providers require a return for bearing ownership risk. WACC combines those costs according to their proportions in the business's capital structure. It is an economic funding benchmark rather than a bill the company pays each year.

The NYU Stern notes on discount-rate inputs define WACC using the costs of financing components and their market-value weights. They also distinguish the after-tax cost of debt from the cost of equity.

This example uses only debt and common equity. If the funding workbook includes preferred equity or another separately priced capital source, include its approved cost and weight rather than forcing it into the common-equity line.

WACC = Equity weight × Cost of equity + Debt weight × Pretax cost of debt × (1 - Assumed tax rate)

Debt weight = Debt capital value / Total capital value

Equity weight = Equity capital value / Total capital value

The weights describe shares of capital, not shares of revenue or operating expense. A debt-to-equity ratio compares the same funding categories differently and does not replace those weights.

The workbook rows finance must supply

Start with an approved capital schedule and an assumptions sheet. Keep the entity, currency, valuation date, value basis, annual cost, tax treatment, and assumption owner visible. Debt and equity values must describe the same business boundary at the same date.

Use supplied current cost assumptions appropriate to the question. Historical interest expense divided by closing debt can mix periods, fees, average balances, and old borrowing terms. The equity cost is a required return assumption, not an accounting expense or the dividend rate.

For conventional WACC, use supplied market-value weights. If a private business uses approved target weights or an internal proxy, label that basis and its limits. Do not silently present a book-equity balance as a current market value.

The wider capital structure ratios review addresses leverage measures; this calculation focuses on how the chosen capital weights combine with funding costs.

A worked business funding example

A US equipment manufacturer supplies the following capital assumptions as of October 23, 2026. Values are approved estimates on a consistent basis for this illustration. The 25.0% tax rate is a supplied planning assumption, not a statement of the company's statutory tax rate or a tax calculation.

The assumed adjustment applies to debt only. Equity's required return remains 12.0%. Calculate each capital weight and multiply it by its applicable cost:

For a spreadsheet with Capital value in B, Supplied cost in C, and Assumed tax rate in D, place debt on row 2 and equity on row 3. Use these formulas for the respective contributions and total:

=B2/SUM($B$2:$B$3)*C2*(1-D2)
=B3/SUM($B$2:$B$3)*C3
=SUM(E2:E3)

The first two formulas belong in E2 and E3. Format results as percentages. This example displays rates to one decimal place and retains unrounded values in the calculations.

Prove the rate with a funding charge

Multiply each capital value by its applicable annual cost. This converts the weighted-rate arithmetic into a dollar reconciliation:

The identity is $900,000 / $10,000,000 = 9.0%. Also check that the weights total 100.0% and that each capital value ties to the approved schedule. The equivalent equity charge is not a promised dividend or a cash payment forecast.

The tax benefit needs separate review. The IRS guidance on business interest expense limitations explains that deductions may be limited. The tax owner must confirm whether the simplified assumed reduction is usable; the WACC formula does not establish eligibility.

Compare supplied assumptions and assign ownership

Change one input at a time to understand the result. Keep the capital values and the assumed tax rate from the first table:

These are sensitivity cases, not predictions. Treasury owns borrowing assumptions and capital values; the CFO or delegated finance owner approves equity assumptions and the intended use; tax reviews the debt adjustment. FP&A reconciles the workbook and explains what changed.

WACC may inform a capital planning discussion, but the appropriate benchmark also depends on project risk and cash-flow definitions. Use capital budgeting cash flow analysis for the project cash-flow work rather than treating this funding table as an investment recommendation.

Where it goes wrong

• Mixing value bases or dates. A current equity estimate and an old debt schedule produce weights with no consistent basis.
• Using total liabilities as debt. Confirm which financing obligations belong in the approved capital definition.
• Assuming every interest deduction is usable. The tax adjustment needs support for the business and period.
• Treating more debt as automatically cheaper. Borrowing and required equity costs can both change with leverage.
• Reading WACC as cash interest. The equity component is an economic return requirement, not an interest invoice.

Compare your funding workbook in Covirage

Upload a sample of your own capital schedule and supplied cost assumptions to Covirage. Covirage maps the columns, and its tools compute and check the underlying workbook figures; the external AI model explains the comparisons with every figure traced to its rows. Create a free Covirage account and bring a sample of your own data.

See Covirage for finance teams for the supporting workflow.