When choosing a discount rate for a DCF model, what matters most?

• A. Always use the highest possible rate to ensure conservative valuation.
• B. Use the cost of debt only.
• C. Use the average inflation rate.
• D. Choose a rate that reflects risk and capital structure (WACC); an inappropriate rate distorts valuation and decision-making.

Answer: (D)

In a DCF, the discount rate should reflect the risk of the cash flows and how the project or firm is financed. That means using the blended cost of capital from all sources—the weighted average cost of capital (WACC)—because it captures the opportunity cost for both debt and equity investors and incorporates the tax shield from debt. If you set the rate too high or too low, you distort present value, leading to systematically faulty valuations and misguided decisions. Using just the cost of debt ignores equity risk and financing structure, while inflation or always choosing the highest rate ignores the actual risk level of the cash flows. The key is to pick a rate that matches the risk of the cash flows and the firm’s financing mix, typically expressed as the WACC for unlevered cash flows (or the cost of equity for levered cash flows).