Professor Jessie

What Is Capital Structure?

Every firm needs money to operate and grow. That money comes from two broad sources: debt (borrowing from creditors) and equity (selling ownership stakes to shareholders). The specific mixture of debt and equity a firm uses is its capital structure — and choosing the right mix is one of the most consequential decisions a financial manager makes.

Two Forces Shape the Decision

• Tax deductibility of interest — Interest payments on debt are tax-deductible, creating a "tax shield" that effectively lowers the cost of debt. Dividend payments to equity holders are not deductible. This creates a structural advantage for debt.
• Bankruptcy and financial distress risk — As debt increases, so does the fixed obligation to make interest and principal payments. If the firm's cash flow can't cover those payments, it faces bankruptcy — a costly and destructive outcome.

The entire chapter explores the tension between these two forces. More debt means more tax benefit but also more risk. Less debt means more safety but also a higher tax burden. Finding the optimal balance is the art and science of capital structure management.

Active vs. Passive Capital Structure Changes

Firms don't just set a capital structure once and forget it. The debt-to-equity mix evolves over time, and managers have two fundamentally different approaches for deliberately changing it.

Which Approach Is Better?

It depends on three factors: how quickly the firm is growing (fast growth favors passive — there are more new projects to fund with the preferred capital type), how high flotation costs are (high costs favor passive), and how urgently the firm wants to change its capital structure (urgent needs favor active). For businesses expecting to add significant assets soon, the passive approach usually wins — it achieves the desired shift without paying for two separate transactions.

Financial Leverage: Why Debt Is Called "Leverage"

Finance professionals routinely refer to debt as leverage — and the metaphor is precise. A lever magnifies force: a small push on one end produces a large movement on the other. In finance, debt does the same thing to returns.

How Leverage Works

When a firm uses debt, it magnifies both the expected return and the risk (variability) of returns to equity holders. Here's the mechanism: debt holders receive a fixed interest payment regardless of how well the firm performs. Whatever is left — whether a large profit or a small one — goes to equity holders. The fixed nature of debt payments acts as a fulcrum:

• When times are good: The firm earns a high return on its assets, pays the fixed interest to bondholders, and equity holders capture the entire surplus. Return on equity soars.
• When times are bad: The firm earns a low return, but it still owes the same fixed interest payment. Equity holders absorb the entire shortfall. Return on equity collapses — potentially going negative even when the firm is still modestly profitable.

Modigliani-Miller: The "Perfect World" Theorem

In 1958, Franco Modigliani and Merton Miller published a theorem that revolutionized corporate finance. Their core claim was startling: in a perfect world, the value of a firm is completely independent of its capital structure. How the firm is financed — all equity, all debt, or any mix — doesn't matter at all.

The "Perfect World" Assumptions

• No taxes — No corporate income tax, no personal tax
• No possibility of bankruptcy — Firms never fail to meet obligations
• Perfectly efficient markets — All information is freely available, no transaction costs
• Symmetric information — Managers and investors know exactly the same things

Proposition 1: Firm Value Irrelevance

The value of a leveraged firm (one with debt) equals the value of an unleveraged firm (all equity). In a perfect world, the firm is worth the same no matter how it's financed. Why? Because investors can replicate any capital structure on their own through personal borrowing and lending — the firm's financing choice adds no value that investors couldn't create themselves.

Proposition 2: Cost of Equity Rises with Debt

As the firm takes on more debt, the cost of equity capital increases — equity holders demand higher returns to compensate for the additional risk leverage creates. However, this increase is exactly offset by the lower cost of debt. The result: WACC stays constant regardless of the debt-to-equity ratio. The firm's overall cost of capital doesn't change.

M&M with Corporate Taxes: The Tax Shield

Now we relax one assumption: we allow corporate taxation. Specifically, we assume corporations are taxed, corporate debt is perpetual, interest is tax-deductible, and the firm can fully utilize its interest tax shields. This single change transforms the conclusion.

Debt Creates Value Through Tax Shields

Because interest payments are tax-deductible, every dollar of interest the firm pays reduces its tax bill. This tax shield represents real cash savings. The value of a leveraged firm becomes:

Where V_L is the value of the leveraged firm, V_U is the value of the unleveraged (all-equity) firm, D is the level of perpetual debt, and T_C is the corporate tax rate. The term (D × T_C) is the present value of the perpetual tax shield.

The Startling Implication

Under this model, the more debt the firm uses, the more valuable it becomes. The relationship is linear — every additional dollar of debt adds T_C dollars of value. Taken to its logical conclusion, the firm should be 100% debt-financed. This is clearly not what we observe in the real world, which means something else must be holding firms back from maximum leverage.

Homemade Leverage and the Re-leverage Choice

If a firm changes its capital structure, what happens to investors who preferred the old structure? M&M's answer is elegant: in efficient markets, investors can undo or replicate any capital structure change on their own.

How Homemade Leverage Works

If a firm increases its debt and an investor prefers the old, less-leveraged profile, the investor can simply lend money (buy bonds) to offset the firm's increased leverage in their personal portfolio. Conversely, if a firm decreases debt and the investor wants more leverage, they can borrow on margin to replicate the effect. This is called homemade leverage.

The implication is profound: because investors can adjust their own leverage costlessly, the firm's capital structure choice doesn't create value for them — they can always replicate it themselves. This reinforces Proposition 1's irrelevance result.

Break-Even EBIT: The Indifference Point

One practical tool for comparing capital structures is the EBIT-EPS indifference analysis. It identifies the specific EBIT (Earnings Before Interest and Taxes) level at which shareholders would be equally well off under two different capital structures.

The Process

• Step 1: Express EPS (Earnings Per Share) for each capital structure as a function of EBIT.
• Step 2: Set the two EPS expressions equal to each other.
• Step 3: Solve for the break-even EBIT — the level where EPS is identical under both structures.

Below the break-even EBIT, the all-equity structure produces higher EPS (no interest payments dragging down earnings). Above the break-even, the leveraged structure wins (the fixed interest cost is small relative to the large operating income, and the fewer shares outstanding magnify EPS). The break-even point is the tipping point where leverage switches from harmful to helpful.

Bankruptcy: Chapter 7 and Chapter 11

When a firm can't meet its debt obligations, it enters bankruptcy. The US legal system provides two main paths, each with very different consequences for the firm and its stakeholders.

The Absolute Priority Rule

In liquidation, claimants are paid in a strict order. Jumping the queue is not allowed:

The Costs of Financial Distress

Bankruptcy itself is expensive, but the damage starts well before a firm actually files for bankruptcy. The costs of financial distress begin mounting the moment a firm's solvency comes into question:

• Loss of customer confidence — Buyers worry about warranty support, parts availability, and future service. Why buy software from a company that might not exist next year?
• Tighter supplier credit — Sellers demand cash on delivery instead of extending trade credit, draining the firm's working capital at the worst possible time
• Lost partnerships — Other firms hesitate to enter strategic alliances or joint ventures with a financially shaky partner
• Brain drain — Top employees leave for safer employers, eroding the firm's human capital and operational efficiency

Overinvestment and Underinvestment

When equity is nearly worthless, equity holders face perverse incentives that can destroy firm value:

The Trade-Off Theory: Finding the Optimal Mix

Now we combine both forces. With corporate taxes but no bankruptcy costs, more debt is always better (linear value increase from the tax shield). With bankruptcy costs but no taxes, more debt is always worse. With both taxes and bankruptcy costs, we get a trade-off — and an optimal capital structure emerges.

The Two Competing Forces

• Tax shield benefit: Linear and increasing — each dollar of debt adds T_C dollars of value
• Financial distress costs: Nonlinear and convex — costs start small but accelerate rapidly as debt increases and bankruptcy probability rises

The total value of the leveraged firm becomes:

At low debt levels, the tax shield dominates — adding debt increases value. At high debt levels, distress costs dominate — adding debt destroys value. The optimal capital structure is the point where the marginal tax benefit of one more dollar of debt exactly equals the marginal expected cost of financial distress from that dollar. This is the "sweet spot" that maximizes firm value.

Capital Structure Theory vs. Reality

The trade-off theory provides a elegant framework, but do real-world firms actually behave this way? The evidence is mixed — firms' capital structures are influenced by factors the model doesn't fully capture.

What the Theory Predicts

• High-tax firms should use more debt — The tax shield is more valuable when tax rates are high, so firms facing higher effective tax rates should lever up more
• Stable-income firms should use more debt — Firms with predictable cash flows (utilities, consumer staples) can handle more debt safely because their income reliably covers interest payments
• Risky, volatile-income firms should use less debt — Tech startups and cyclical manufacturers face high bankruptcy risk, so they should rely more on equity

What We Actually Observe

Average debt-to-equity ratios vary dramatically across sectors, generally consistent with the theory — but with important deviations:

Key Takeaways

• Capital structure = the mix of debt and equity used to finance the firm
• Two approaches to changing it: active (restructuring — swap debt for equity) and passive (fund new projects with the preferred capital type)
• Debt is called "leverage" because it magnifies both returns and risk for equity holders
• M&M Proposition 1 (perfect world): Firm value is independent of capital structure
• M&M Proposition 2: Cost of equity rises with debt, but WACC stays constant
• With corporate taxes, debt creates value through the interest tax shield: V_L = V_U + D×T_C
• Homemade leverage: Investors can replicate any capital structure, so financing choices only matter for things investors can't replicate (tax shields, bankruptcy costs)
• Break-even EBIT identifies the tipping point where leverage becomes beneficial
• Bankruptcy (Chapter 7 = liquidation, Chapter 11 = reorganization) and financial distress impose real, increasing costs
• The trade-off theory balances tax benefits against distress costs to find an optimal debt level
• Real-world capital structures broadly follow the theory but are also shaped by flexibility, signaling, and market timing considerations