Subordinated debt (sub debt) is any debt instrument that ranks below senior debt in the payment waterfall — it is "subordinate" to senior claims in both ongoing payments and in a liquidation or bankruptcy. The subordination may be structural (junior holding company debt vs. senior operating company debt), contractual (agreed by inter-creditor agreement), or by operation of law (unsecured vs. secured claims).
Common forms of subordinated debt include second-lien loans, mezzanine loans, high yield bonds (when junior to bank debt), PIK notes, subordinated promissory notes, and seller notes. Each carries the same fundamental characteristic: repayment comes after senior lenders are made whole, and in a true insolvency scenario, junior creditors often receive little or no recovery.
The yield premium on subordinated debt compensates investors for two primary risks: lower probability of full repayment (because the borrower's enterprise value must exceed all senior claims before subordinated debt recovers anything) and lower recovery in the event of default (because assets are distributed to senior creditors first). Historical research confirms that subordinated debt — second-lien loans, mezzanine, and high yield bonds in leveraged structures — experiences materially lower recovery rates than first-lien debt in distressed scenarios.
Despite the risk, subordinated debt plays an important role in capital structure optimization. It allows borrowers to maximize the amount of debt in their capital structure by layering in additional debt behind the senior secured tranche, enabling larger transactions, more aggressive buyouts, and higher enterprise valuations in PE transactions. For investors, it offers higher income potential than senior debt with less equity-like risk and volatility than common stock.
Credit analysis of subordinated debt requires modeling the "coverage" — the amount by which the enterprise value must decline before the subordinated debt position is impaired. A subordinated debt investor at 4–7x EBITDA leverage (in a company with first-lien debt at 4x) needs to assess whether the business can support both tranches through the credit cycle and whether there is sufficient enterprise value to repay the subordinated debt at maturity or in a sale/restructuring.