Capital structure refers to the composition of a company's financing — the mix of debt, equity, and hybrid instruments used to fund its assets and operations. For credit professionals, understanding capital structure means knowing not just what a company owes, but to whom it owes it, in what form, at what priority, and what rights each creditor holds in various scenarios.
At its simplest, capital structure is a stack. At the top are the highest-priority, lowest-risk claims: secured debt, which is backed by liens on specific assets and has first claim on those assets in a liquidation. Below secured debt sits unsecured senior debt — senior notes, debentures, and trade payables — with a general claim on the company's assets but no specific collateral. Below that sits subordinated debt, preferred equity, and finally common equity, which bears the most risk but receives all residual value if the business exceeds its debt obligations.
The classic finance framework — the Modigliani-Miller theorem — suggests that in a world without taxes or distress costs, capital structure is irrelevant to firm value. In the real world, however, debt's tax deductibility of interest creates a "tax shield" that incentivizes borrowing, while distress costs (legal fees, management distraction, customer/supplier concern, loss of investment-grade access) create offsetting costs. The optimal capital structure balances these trade-offs.
For leveraged transactions, capital structure is engineered to maximize the total amount of debt a business can support, thereby reducing the equity investment required and increasing potential equity returns. Sponsors model the capital structure to ensure that projected cash flows service all debt tranches through the investment period, while maintaining covenant headroom and preserving liquidity for operational needs.
From a credit analyst's perspective, the most important capital structure analysis is the "waterfall" — the distribution of value in a stressed or bankruptcy scenario. Mapping enterprise value against each debt layer reveals which creditors are "in the money" (their claims are covered by enterprise value), which are "at the money" (barely covered), and which are "out of the money" (impaired). This analysis drives valuation, trading prices, and restructuring negotiations.