Capital Structure and Leverages

What capital structure means and why it is contested

Capital structure is the mix of long-term sources of finance a firm uses — the proportion of debt to equity in particular. This chapter asks a question that sounds simple but is genuinely contested in finance theory: does the specific mix of debt and equity a firm chooses affect the firm's overall value and its cost of capital, or is value determined entirely by the firm's assets and earning power, with the financing mix being irrelevant?

The chapter builds on the previous one directly. WACC was computed there by weighting each source's specific cost by its proportion in the capital structure; this chapter asks whether, as that proportion itself changes — as a firm takes on more or less debt — the specific costs of equity and debt shift in response, and whether some particular mix minimises the resulting WACC and thereby maximises firm value.

Net Income approach

The Net Income (NI) approach holds that capital structure does matter, and that a firm can lower its overall cost of capital and raise its value simply by using more debt. The reasoning is that the cost of debt is cheaper than the cost of equity — debt holders bear less risk than equity holders and are paid first, and interest is tax-deductible on top of that — so as a firm substitutes debt for equity, holding the specific cost of each source constant regardless of how much debt is used, WACC mechanically falls, because a larger weight is placed on the cheaper source. Under this approach, WACC keeps falling and firm value keeps rising as debt increases, implying the firm should, in the limit, use as close to 100% debt financing as possible.

Net Operating Income approach

The Net Operating Income (NOI) approach takes the opposite position: capital structure is irrelevant to the overall value of the firm and to WACC. The reasoning is that while debt itself is cheaper than equity, using more debt increases the financial risk borne by equity shareholders, since a larger proportion of fixed obligations must be met before anything is left for equity, and equity shareholders respond by demanding a correspondingly higher cost of equity as leverage rises. Under this approach, the rising cost of equity exactly offsets the benefit of substituting in cheaper debt, so that WACC remains constant regardless of the debt-equity mix, and overall firm value is determined solely by its operating earnings and the risk of the business itself, not by how those earnings happen to be financed.

Traditional approach

The traditional approach sits between these two extremes, and is the view most consistent with practical experience. It holds that a firm can indeed lower its WACC and raise its value by using more debt, but only up to a point. In the early stages of increasing leverage, the benefit of substituting cheaper debt for more expensive equity dominates, and WACC falls as debt increases, exactly as the NI approach predicts. Beyond a certain level of leverage, however, the market begins to perceive the firm's financial risk as materially elevated, and both the cost of equity and, eventually, the cost of debt itself begin to rise more steeply to compensate lenders and shareholders for this now-material risk, and this rising cost eventually more than offsets the benefit of the cheaper debt weight, causing WACC to rise again. The traditional approach therefore implies an optimal capital structure — a specific debt-equity mix at which WACC is minimised and firm value is maximised — located at the point just before the rising cost of capital begins to outweigh the benefit of additional cheap debt.

Modigliani-Miller propositions

Modigliani and Miller (MM) formalised the NOI approach's intuition with rigorous theoretical propositions, first under the idealised assumption of no taxes, and then extended to incorporate taxes.

MM Proposition I, without taxes, states that the value of a levered firm equals the value of an identical unlevered firm — capital structure is irrelevant to firm value in a world with no taxes, no bankruptcy costs, and perfect capital markets, because investors can replicate or undo any leverage the firm chooses through their own personal borrowing or lending, a mechanism called homemade leverage, making the firm's own financing choice unable to create any value the investor could not already achieve independently.

MM Proposition I, with taxes, revises this conclusion once corporate tax is introduced: because interest is tax-deductible, debt creates a genuine tax shield — a real cash saving to the firm from the tax deductibility of interest that does not exist for equity — and MM show that the value of a levered firm exceeds the value of an unlevered firm precisely by the present value of this tax shield. Under this version, firm value rises continuously as debt increases, implying, in its purest form, that a firm should be financed almost entirely by debt to maximise the tax shield, a conclusion tempered in practice by costs the pure MM-with-tax model does not capture, most importantly the costs of financial distress and bankruptcy that rise as leverage becomes extreme, which is where the trade-off theory, blending MM's tax shield insight with these real-world costs, arrives at a more moderate, traditional-approach-like conclusion in practice.

Operating, financial and combined leverage

Where the theories above debate whether an optimal capital structure exists, leverage measures quantify the risk that a given capital structure and cost structure actually create, and this is where the paper turns fully numerical.

Operating leverage arises from the presence of fixed operating costs in a firm's cost structure. A firm with high fixed operating costs relative to variable costs experiences a magnified effect on EBIT for a given percentage change in sales, because fixed costs do not move with sales while contribution does. The degree of operating leverage (DOL) measures this magnification:

DOL = % change in EBIT ÷ % change in Sales = Contribution ÷ EBIT

A DOL of 3 means a 1% change in sales produces roughly a 3% change in EBIT. High operating leverage is characteristic of capital-intensive businesses with large fixed costs, such as heavy manufacturing, and makes EBIT more volatile relative to sales.

Financial leverage arises from the presence of fixed financial costs — interest on debt and preference dividend — in a firm's capital structure. A firm financed heavily by debt experiences a magnified effect on earnings per share (EPS) for a given percentage change in EBIT, because fixed financial costs do not move with EBIT. The degree of financial leverage (DFL) measures this:

DFL = % change in EPS ÷ % change in EBIT = EBIT ÷ (EBIT − Interest)

A DFL of 2 means a 1% change in EBIT produces roughly a 2% change in EPS. This is the direct numerical expression of the favourable-leverage idea from the ratio analysis chapter — a positive DFL above 1 means EPS benefits more than proportionately from a rise in EBIT, but it cuts both ways, and a fall in EBIT is equally magnified into a larger fall in EPS.

Combined leverage, sometimes called total leverage, captures the full effect of both operating and financial leverage together, from sales all the way through to EPS:

DCL = DOL × DFL = % change in EPS ÷ % change in Sales

A firm with both high operating leverage and high financial leverage has a very high combined leverage, meaning even a modest change in sales translates into a dramatically magnified change in EPS — a genuinely risky combination, since both sources of magnification compound each other, and this combination is precisely what the method chapter flagged as the most commonly confused pair of terms in this paper: knowing which leverage a question is asking about, and applying the matching formula, is the entire skill this section tests.

EBIT-EPS analysis and indifference point

EBIT-EPS analysis applies these leverage ideas to a specific, frequently examined decision: choosing between financing alternatives, typically debt versus equity, for raising a given amount of fresh capital. The indifference point (or break-even point between financing plans) is the level of EBIT at which two financing alternatives produce the identical EPS, found by setting the EPS formulas for both alternatives equal and solving for EBIT.

Below the indifference point, the alternative with lower fixed financial charges, typically equity financing, produces a higher EPS, because at low EBIT, the burden of fixed interest under the debt alternative more heavily depresses EPS. Above the indifference point, the alternative with higher fixed financial charges, typically debt financing, produces a higher EPS, because the fixed interest cost is now more than covered, and the earnings on the debt-financed portion, in excess of the interest cost, accrue entirely to a smaller base of equity shares outstanding under the debt alternative, magnifying EPS the way financial leverage always does above the point where it becomes favourable. This is why EBIT-EPS analysis is a genuinely decision-useful tool, not merely an abstract computation: a firm's expected EBIT relative to the indifference point tells it directly which financing alternative is likely to serve its shareholders better.

Bringing the chapter together

Capital structure theory debates whether a mix exists that minimises WACC; leverage analysis quantifies the risk any given mix actually creates for EBIT and EPS; and EBIT-EPS analysis applies both together to a live financing choice. None of these tools work in isolation — a firm choosing a capital structure under the traditional approach's logic, seeking the point where WACC is minimised, is implicitly also choosing a level of financial leverage, and that leverage choice is exactly what EBIT-EPS analysis and the degree of financial leverage formula make concrete and numerical. Treat the theories as the reasoning for why a mix might matter, and the leverage formulas as the tools that measure precisely how much risk a specific mix creates.