Capital Structure

Each source of capital carries its own required return, and the firm's overall cost of capital is the weighted average of those returns, with weights equal to the proportion of total capital each source represents. Debt enters after tax: the pre-tax borrowing rate is multiplied by one minus the marginal tax rate, because interest is deductible in most jurisdictions while dividends are not. Preferred stock enters at its dividend divided by its market price. Common equity is typically estimated from a risk-based model such as the capital asset pricing model, or from a dividend growth relationship.

Weights should be based on market values, not balance sheet carrying amounts, because investors price the claims they actually hold. In practice, analysts often use the company's stated target structure when market values are unavailable or when current leverage is clearly temporary.

In a frictionless world with no taxes, no bankruptcy costs and symmetric information, the value of a firm depends on its assets, not on how those assets are financed; substituting debt for equity simply raises the required return on the remaining equity, leaving the weighted average unchanged. Real markets break every one of those assumptions.

Deductible interest creates a tax shield that adds value as leverage rises. Working against it are the expected costs of financial distress: legal and restructuring expenses, lost customers and suppliers, forced asset sales, and the tendency of distressed managers to underinvest or gamble. Agency conflicts cut both ways, since debt disciplines free cash flow but can also encourage risk-shifting at bondholders' expense. The static trade-off view places the optimum where the marginal tax benefit of additional debt equals the marginal cost of distress, which is where the weighted average cost of capital is minimised and firm value maximised.

Companies rarely sit exactly at a theoretical optimum. Under pecking order reasoning, managers prefer internally generated funds first, then debt, then equity issuance last, because outside investors read a share issue as a signal that management considers the stock richly priced. Announced equity offerings therefore often depress share prices, while debt issues are treated as comparatively neutral news.

Structures also cluster by industry and asset base. Utilities and real estate, with stable cash flows and pledgeable tangible assets, sustain high leverage; software and biotechnology firms, whose value lies in intangibles and growth options, run near-zero debt. Credit ratings, covenant packages, legal protections for creditors, the depth of local bond markets and the strength of banking relationships all shape what a given issuer can realistically carry.

Candidates should be able to build market-value weights from a company's outstanding shares and debt, compute the weighted average cost of capital component by component, and explain the direction in which a change in leverage moves each input. Expect questions that trace how added debt raises the required return on equity even as the debt component looks cheap, and that distinguish the cost of capital used for discounting from the accounting interest expense reported on the income statement.

Equally important is judgement about targets. A firm's actual ratios drift with share prices and cash generation, so a stated target structure, or a peer-group average when no target is disclosed, is generally the better basis for valuing projects with long lives. Recognise the signalling content of financing announcements and the conditions under which more leverage stops adding value.