Weighted Average Cost of Capital (WACC)

Last Updated on April 16, 2026 by Admin

The Weighted Average Cost of Capital (WACC) represents the return a company must generate to meet the expectations of both debt and equity investors, given the risk of its underlying business. In effect, it is the opportunity cost of capital applied to the firm.

WACC is calculated as a weighted average of the cost of equity and the after-tax cost of debt, with the weights based on the market value of each funding source. A business is not funded for free. Lenders require compensation through interest, while shareholders expect a return that reflects the uncertainty of future cash flows.

In valuation, WACC is typically used as the discount rate in Discounted Cash Flow (DCF) models. It also provides a practical benchmark for capital allocation. Projects that generate returns above WACC create value, while those below WACC reduce it.

In practice, estimating WACC involves judgement. Inputs such as beta and the equity risk premium are not directly observable and can vary depending on the methodology and data source used. As a result, even small changes in assumptions can have a meaningful impact on valuation outcomes.

While debt is generally cheaper than equity due to the tax deductibility of interest, increasing leverage introduces financial risk. Beyond a certain point, this can increase both the cost of debt and the cost of equity. The relationship between capital structure and WACC is therefore not linear.

For ASX-listed companies, equity typically represents the majority of total capital. As a result, WACC is often driven primarily by the cost of equity rather than the cost of debt. In the current Australian interest rate environment, movements in government bond yields have had a direct impact on WACC assumptions, particularly for capital-intensive sectors such as mining and infrastructure.

Formula

Where:

• E = Market value of equity (market capitalisation)
• D = Market value of debt
• r_e = Cost of equity
• r_d = Cost of debt
• t = Corporate tax rate

Cost of equity (r_e)

The cost of equity is estimated using the Capital Asset Pricing Model (CAPM):

$$r_e = r_f + \beta \times (ERP)$$

Inputs:

• Risk-free rate (r_f): Yield on long-term Australian Commonwealth Government bonds
• Equity risk premium (ERP): Expected excess return of the equity market over the risk-free rate
• Beta (β): Measure of systematic risk relative to the market

Cost of debt (r_d)

The cost of debt reflects the current market borrowing rate of the company, not historical interest expense. It is typically estimated using:

• Yield to maturity on outstanding bonds (preferred), or
• Risk-free rate plus a credit spread based on the company’s credit rating

The cost of debt is adjusted for the tax shield:

$$\text{After-tax cost of debt} = r_d (1 – t)$$

Capital Structure (E/D)

WACC uses market value weights, not book values, to reflect the current economic value of financing.

• Equity is measured using market capitalisation
• Debt is measured at market value, though book value is often used as a proxy when market data is unavailable

Where relevant, equity should be fully diluted to account for options, performance rights, and convertible securities.

Example (BHP)

Market Data:

• Equity (E): AUD$281bn (market cap)
• Debt (D): USD$24.5bn
• FX rate (USD/AUD): 1.55
• Debt (D): AUD$38.0 bn

Capital Structure

• Total capital = 281 + 38 = AUD$319 bn
• Weight of equity = 281 / 319 = 88.1%
• Weight of debt = 38 / 319 = 11.9%

Cost of Equity:

• Risk-free rate: 4.0%
• Equity Risk Premium (ERP): 6.0%
• Beta: 1.1
• r_e = 10.1%

Cost of Debt:

• Pre-tax cost of debt: 5.0%
• Tax rate: 30%
• After-tax r_d = 3.6%

Interpretation

A WACC of approximately 9.2% implies that the company must generate returns above this threshold to create value for investors.

• Return on invested capital (ROIC) > WACC: Value creation
• ROIC < WACC: Value destruction

Notes

WACC is sensitive to assumptions, particularly beta and the equity risk premium

• It assumes a stable capital structure over time
• The discount rate should reflect the risk of the cash flows being valued
• Small changes in WACC can materially impact valuation outcomes

Assumptions

The inputs used in estimating WACC are based on market data and standard valuation assumptions. The risk-free rate is proxied using the yield on long-term Australian government bonds. Beta is estimated using historical market data, and the equity risk premium reflects market-based estimates. The cost of debt is inferred from current borrowing rates, and a corporate tax rate of 30% is assumed.