Exploring the Net Income Approach to Capital Structure

Every company that raises money has to answer one basic question: how much should come from debt, and how much from equity? The answer isn’t just an accounting detail. Depending on which theory of capital structure you subscribe to, that debt-equity mix can change how much the company is worth. The Net Income Approach is one of the earliest and most direct theories that says this mix matters, and it does so in a fairly bold way.

What is the net income approach? 🔗

The Net Income (NI) Approach was proposed by David Durand in 1952 as part of what is often called the “traditional view” of financing decisions. It argues that a firm’s capital structure is directly relevant to its value. In simple terms, if a company changes its debt-equity ratio, its overall cost of capital and its market value change too, and not just as a side effect but as a deliberate, usable lever.

The core claim is straightforward: since debt is cheaper than equity, increasing the proportion of debt in the capital structure lowers the firm’s weighted average cost of capital (WACC). A lower WACC, in turn, pushes the value of the firm upward. Taken to its logical extreme, this approach suggests that a firm could keep increasing its value right up to the point where it is financed almost entirely by debt, since the optimal capital structure under this theory is one with the highest possible proportion of debt.

This is quite different from theories that argue capital structure is irrelevant to a firm’s value, such as the Net Operating Income Approach. The NI Approach sits firmly in the camp that says financing choices are not neutral, they actively shape shareholder wealth, as outlined in the study material on capital structure decisions and firm value.

The assumptions the model rests on 🔗

Like most early financial theories, the Net Income Approach simplifies reality quite a bit to make its argument clean. These simplifications are exactly what later theories, including Durand’s own later work, went on to question. The main assumptions are:

• Debt is always cheaper than equity: The cost of debt (Kd) is lower than the cost of equity (Ke), and this relationship holds no matter how much debt the firm takes on.
• Financing costs stay fixed: Both Kd and Ke remain constant regardless of how the debt-equity ratio changes. Adding more debt doesn’t make lenders or shareholders nervous enough to demand a higher return.
• Investor risk perception doesn’t shift: Even as leverage rises, investors don’t reassess the riskiness of the firm. This is one of the more heavily criticised assumptions of the approach.
• No corporate taxes: The model ignores the tax-deductibility of interest, which in reality is one of the biggest reasons companies prefer some level of debt financing.
• Only two sources of capital: The firm is financed purely through debt and equity, with no preference share capital or retained earnings entering the calculation.
• Total capital requirement stays constant: The overall size of the firm’s capital base doesn’t change; only the debt-equity mix within it does.

These conditions are laid out in detail in academic course material on capital structure theories, which walks through why each assumption is necessary for the approach’s conclusions to hold.

How the numbers actually work 🔗

The mechanics of the Net Income Approach come down to three formulas, all built around the idea that a firm’s earnings, once interest is paid out, define what shareholders are entitled to.

The core formulas 🔗

A worked example 🔗

Suppose a company has an EBIT of ₹5,00,000, a cost of equity (Ke) of 15%, and can borrow at an after-tax cost of debt (Kd) of 10%. Here is what happens to its value as it takes on more debt, keeping EBIT unchanged.

Notice what happens as debt increases: even though Net Income itself falls (because of the interest burden), the total value of the firm keeps rising, and the overall cost of capital keeps falling. This is the entire logic of the Net Income Approach in one table. Cheap debt is replacing more expensive equity fast enough that the firm’s blended cost of financing drops, and the market rewards that with a higher valuation.

Why this matters for financial decision-making 🔗

For a finance manager, the Net Income Approach offers a tempting proposition: if debt is cheaper, use more of it, and the firm’s value goes up almost automatically. This kind of thinking shows up in real capital structure decisions, particularly for companies that have stable, predictable cash flows and can comfortably service higher debt without alarming lenders or shareholders.

It also explains why leverage is often treated as a tool rather than just a financing necessity. A firm expanding through debt isn’t only trying to avoid diluting ownership through fresh equity issues, it may also be trying to lower its blended cost of capital in exactly the way this theory describes. Empirical work on firms in South Asia has found that several companies do lean on something close to this reasoning when structuring their financing, even if the underlying assumptions are never fully true in practice, as discussed in research on determinants of capital structure among listed companies.

This has a practical flavour too. Indian companies with steady, asset-backed cash flows, think power generation, infrastructure, or established manufacturing, have historically been able to raise debt at relatively stable rates precisely because lenders view their earnings as predictable. In such cases, moderately increasing leverage genuinely can lower the blended cost of financing, mirroring what the Net Income Approach predicts, at least until the firm’s debt burden starts looking risky to lenders and rating agencies. A finance manager evaluating a fresh round of funding still asks a version of the same question this seventy-year-old theory poses: will the next rupee of debt cost less than the next rupee of equity, and will it actually bring the firm’s blended cost of capital down?

Where it breaks down 🔗

The trouble is that none of the assumptions behind the Net Income Approach hold up cleanly in the real world. Lenders don’t keep offering debt at the same interest rate no matter how much a firm borrows. Once leverage crosses a certain threshold, both debt and equity investors start pricing in the added financial risk, pushing Kd and Ke upward rather than leaving them constant. Corporate taxes exist almost everywhere, which actually makes debt even more attractive than this model assumes, since interest payments are tax-deductible. And bankruptcy isn’t costless. A heavily indebted firm faces real risk of financial distress, something this approach doesn’t factor in at all.

This is exactly the gap that later theories tried to close. The Net Operating Income Approach swung to the opposite extreme, arguing that capital structure is irrelevant to firm value. The Traditional Approach, proposed by Ezra Solomon, tried to find a middle ground, suggesting that a firm’s cost of capital does fall as debt increases, but only up to an optimal point, beyond which the risk of over-leveraging pushes costs back up, a distinction well laid out in comparative notes on capital structure theories. Later still, Modigliani and Miller built a more rigorous framework that examined what happens both with and without corporate taxes, a debate that academic literature on capital structure theory continues to revisit even today.

How it fits into the bigger picture 🔗

Despite its unrealistic assumptions, the Net Income Approach isn’t just a textbook relic. It remains the starting point for understanding why leverage can be value-accretive in the first place, a foundation that later, more sophisticated models build on rather than discard. Financial management syllabi, including material referenced by the Institute of Chartered Accountants of India, still open the topic of capital structure with this approach precisely because it isolates the basic mechanism, cheap debt replacing expensive equity, before layering on the complications of taxes, bankruptcy costs, and shifting investor perceptions that more advanced theories address.

Understanding it well also makes the later theories easier to grasp. Once you see how the Net Income Approach pushes firm value up purely through the mechanics of a fixed Ke and Kd, you can appreciate exactly what the Net Operating Income Approach removes from the picture, and exactly what the Traditional Approach and the Modigliani-Miller propositions add back in, whether that’s tax shields, financial distress costs, or a rising cost of equity as leverage increases, as summarised in this overview of capital structure theory.

What do you think? 🔗

What do you think? If cheaper debt really does lower a firm’s overall cost of capital, why don’t more companies push their leverage as close to 100% debt as this theory suggests? And looking at the worked example above, at what point do you think the assumption of a constant cost of equity would realistically start to break down for a growing company?

References

1. https://efinancemanagement.com/financial-leverage/capital-structure-theory-net-income-approach
2. https://www.lkouniv.ac.in/site/writereaddata/siteContent/202003291621086976vijayshankarpandey_Capital_Structure_Theory.pdf
3. https://courseware.cutm.ac.in/wp-content/uploads/2020/05/capital-structure.pdf
4. https://www.nepjol.info/index.php/JNBS/article/view/34/116
5. https://collegehive.in/docs/2nd_sem/site/FM/Unit-3%20Capital%20Structure/3.6%20theories%20of%20capital%20structure.html
6. https://www.sciedu.ca/journal/index.php/afr/article/download/10965/6701
7. https://shop.igpinstitute.org/insight/wp-content/uploads/2024/12/Chapter-5-Financing-Decisions-%E2%80%93-Capital-Structure.pdf
8. https://study.com/academy/lesson/what-is-capital-structure-theory-definition-overview.html