A company’s capital structure is the mix of debt and equity it uses to finance its assets. Should a growing manufacturer borrow from banks, issue bonds, sell new shares or keep reinvesting profits? The choice affects the company’s risk, its cost of capital, its flexibility and, under some conditions, its value. Capital structure is one of the most studied questions in corporate finance, and the answer is not "as much cheap debt as possible".
What you will learn
- Explain the Modigliani–Miller propositions and what they teach
- Understand the tax benefit of debt and the costs of financial distress
- Compare the trade-off and pecking order theories
- Use EBIT-EPS analysis to compare financing options
Why capital structure matters
Debt is usually cheaper than equity because lenders face less risk and interest is often tax-deductible. But debt creates fixed obligations. If cash flows fall, interest and principal must still be paid. More debt therefore raises financial risk for shareholders and, beyond some point, the risk of financial distress. The decision is a balance between these effects.
Modigliani and Miller: the starting point
In 1958 Franco Modigliani and Merton Miller showed that, in a world with no taxes, no bankruptcy costs, no transaction costs and perfect information, the value of a firm does not depend on its capital structure.
- Proposition I: the value of a levered firm equals the value of an identical unlevered firm. Slicing the same cash flows differently between lenders and shareholders cannot create value.
- Proposition II: the cost of equity rises linearly with leverage. As more cheap debt is added, shareholders bear more risk and demand a higher return, exactly offsetting the benefit of cheaper debt, so WACC stays constant.
The theorem does not describe the real world; its value is in showing where capital structure can matter: taxes, distress costs, information and incentives.
Taxes: the benefit of debt
Because interest is generally tax-deductible, debt creates an interest tax shield. With corporate taxes, Modigliani and Miller showed that:
Value with corporate taxes (MM, 1963)
Value of levered firm = Value of unlevered firm + T × D
where T is the corporate tax rate and D the amount of permanent debt. T × D is the present value of the tax shield on permanent debt.
Worked example: the tax shield
An all-equity firm is worth 1,000 (illustrative figures). It borrows 400 permanently and uses the money to buy back shares. The tax rate is 25%.
Value of levered firm = 1,000 + 0.25 × 400 = 1,100.
The extra 100 is the present value of taxes saved. Taken alone, this suggests firms should borrow as much as possible — which they clearly do not, because debt also has costs.
The costs of financial distress
As debt rises, so does the probability that the firm will struggle to meet its obligations. Costs include:
- Direct costs of bankruptcy or restructuring: legal, administrative and advisory fees.
- Indirect costs: lost customers and suppliers, staff departures, forced asset sales at low prices, and management distraction.
- Agency costs: managers acting for shareholders may take excessive risks or pass up good projects when the benefits would mostly go to lenders.
These costs are larger for firms with intangible assets, specialised products and volatile cash flows, and smaller for firms with tangible, easily sold assets and stable revenues.
The trade-off theory
The trade-off theory says firms choose a target debt level that balances the tax benefits of debt against the expected costs of financial distress.
The trade-off theory of capital structure
Show the data
| Series | Debt as % of total capital | Firm value |
|---|---|---|
| Value with tax shield only | 0% | 1,000 |
| Value with tax shield only | 60% | 1,150 |
| Value including distress costs | 0% | 1,000 |
| Value including distress costs | 10% | 1,023 |
| Value including distress costs | 20% | 1,042 |
| Value including distress costs | 30% | 1,052 |
| Value including distress costs | 40% | 1,048 |
| Value including distress costs | 50% | 1,025 |
| Value including distress costs | 60% | 980 |
This explains why profitable firms with stable cash flows and tangible assets (such as utilities) tend to carry more debt, while technology firms with volatile earnings and intangible assets tend to carry less.
The pecking order theory
The pecking order theory starts from information asymmetry: managers know more about the firm’s prospects than outside investors. Issuing new shares can signal that managers think the shares are overvalued, so share prices tend to fall on the announcement. Firms therefore prefer:
- Internal funds (retained earnings) first,
- then debt,
- and new equity only as a last resort.
This explains why highly profitable firms often have little debt: they simply do not need to borrow. Real firms show elements of both theories.
EBIT-EPS analysis
A practical tool for comparing financing options is EBIT-EPS analysis, which shows how earnings per share change with operating profit (EBIT) under different financing plans.
Worked example: debt or equity for an expansion
A company with 1,000,000 shares and no debt needs 5,000,000 for an expansion. It can issue 250,000 new shares at 20 each, or borrow at 10%. The tax rate is 25% (illustrative figures).
At an expected EBIT of 2,000,000:
| Equity plan | Debt plan | |
|---|---|---|
| EBIT | 2,000,000 | 2,000,000 |
| Interest | 0 | 500,000 |
| Profit before tax | 2,000,000 | 1,500,000 |
| Tax (25%) | 500,000 | 375,000 |
| Profit after tax | 1,500,000 | 1,125,000 |
| Shares | 1,250,000 | 1,000,000 |
| EPS | 1.20 | 1.125 |
Indifference EBIT: EPS is equal when (EBIT − 0) × 0.75 ÷ 1,250,000 = (EBIT − 500,000) × 0.75 ÷ 1,000,000, which gives EBIT = 2,500,000. Above that level, the debt plan gives higher EPS; below it, the equity plan does. The EBIT-EPS calculator finds this point for any inputs.
Higher EPS from debt comes with higher risk: EPS under the debt plan falls faster if EBIT disappoints. That is the effect of financial leverage, explained in operating and financial leverage.
What else firms consider
- Flexibility — keeping spare borrowing capacity for future opportunities.
- Credit rating targets and lenders’ covenants.
- Control — issuing shares dilutes existing owners.
- Market conditions — firms tend to issue shares when prices are high and borrow when rates are low.
- Industry norms and the stability of cash flows.
Leverage can be measured with solvency ratios such as debt-to-equity; see also the debt-to-equity calculator.
Common mistakes
- Treating debt as cheap money without accounting for its effect on the cost of equity and on risk.
- Judging a financing plan only by expected EPS, ignoring how variable EPS becomes.
- Using book values when market values of equity are very different.
- Ignoring loan covenants that limit future flexibility.
Key terms
- Capital structure — the mix of debt and equity financing.
- Interest tax shield — the reduction in tax from deductible interest.
- Financial distress costs — direct and indirect costs of difficulty meeting obligations.
- Trade-off theory — firms balance tax benefits against distress costs.
- Pecking order theory — firms prefer internal funds, then debt, then equity.
Frequently asked questions
Is there an optimal capital structure?
Theory suggests a range in which tax benefits and distress costs are balanced. In practice it varies by industry, firm and circumstances, and is estimated rather than calculated precisely.
Why do some very profitable firms have no debt?
Pecking order theory suggests they can fund investment from retained earnings. They may also value flexibility or face few tax benefits from extra debt.
Does borrowing always increase EPS?
Only when the return on the borrowed funds exceeds the after-tax cost of debt — in the example, when EBIT is above the indifference point.
Key takeaways
- Without taxes and frictions, capital structure does not change firm value (Modigliani–Miller).
- The interest tax shield adds value; financial distress costs reduce it.
- Trade-off theory points to a moderate, firm-specific debt level; pecking order explains a preference for internal funds.
- EBIT-EPS analysis shows when debt raises EPS — and how much more volatile EPS becomes.