The Mathematics of Cash Flow Waterfalls and Coverage Ratios
The "Cash Flow Waterfall" is the mechanical algorithm that dictates the priority of every dollar earned by the project.
In Project Finance, this is not merely a guideline but a strict legal mandate embedded in the Common Terms Agreement (CTA). The waterfall ensures that "Systemic Risk" is managed by prioritizing essential outflows. At the top of the waterfall are Operating Expenses (OpEx) and taxes; if these are not paid, the project ceases to function. Below OpEx sits the Senior Debt Service, comprising scheduled interest and principal payments.
To quantify the safety of these payments, analysts use the Debt Service Coverage Ratio (DSCR). The technical formula is defined as $DSCR = \frac{CFADS}{Debt Service}$, where $CFADS$ (Cash Flow Available for Debt Service) is the net cash remaining after OpEx and tax but before any capital expenditures or dividends. Lenders typically mandate a minimum DSCR of $1.20x$ to $1.50x$.
If the ratio drops below this "covenant" level, a "Lock-up" occurs, preventing any cash from being distributed to equity sponsors. This document also details the Loan Life Coverage Ratio (LLCR), which looks forward over the entire remaining life of the loan, using the "Net Present Value" (NPV) of future cash flows to determine if the project remains solvent in the long term, accounting for the "Time Value of Money."