A Collateralized Loan Obligation's internal mechanics are governed by the CLO indenture — the legal contract between the CLO manager, the trustee, and the noteholders. At the core are three interrelated systems: the reinvestment period (which governs how principal is managed), the waterfall (which governs how cash is distributed), and the coverage tests (which govern when distributions to junior tranches are restricted).
The reinvestment period — typically four to five years from the CLO's closing date — is the phase during which the CLO manager can reinvest principal repayments from loan repayments, sales, and amortization into new eligible loans. This reinvestment authority allows the CLO manager to maintain a stable pool of loans throughout the investment period, keeping the CLO's assets and cash flows fully deployed. After the reinvestment period ends, principal collected on loans is used to repay notes in order of priority rather than being reinvested.
The cash flow waterfall defines the priority in which collections from the loan portfolio are distributed. Interest collections flow down the interest waterfall in strict priority: senior expenses (trustee, admin) → AAA note interest → AA note interest → continuing down through each rated tranche → subordinated management fee → equity distributions. Principal collections flow down the principal waterfall similarly. At each step, if any coverage test is failing, the waterfall diverts cash upward to repay senior notes, starving junior tranches of income.
Coverage tests are the CLO's self-correcting risk management tools. The Overcollateralization (OC) test for each note class compares the par value of performing assets in the portfolio to the outstanding balance of that note class and all more senior note classes. If the OC test fails — because of defaulted assets reducing par, assets being sold at a discount, or excessive downgrade of assets to CCC — the waterfall diverts interest that would otherwise flow to junior tranches and equity, using it instead to pay down senior notes until the test is restored.
The Interest Coverage (IC) test measures whether the portfolio generates sufficient interest income to cover note interest. IC test failures are less common than OC test failures but can occur if the portfolio's weighted average spread compresses below the note's required coverage level. Managers actively manage portfolio composition to keep the portfolio spread above the IC test threshold, since test failures directly impair equity distributions.