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Home / Financial Tools / Project Finance Debt Sizing & Cash Flow Waterfall Engine

Graduate-Level Modeling · Project & Infrastructure Finance

Project Finance Debt Sizing & Cash Flow Waterfall Engine

A level amortization schedule leaves debt capacity on the table. Sculpting to a target coverage ratio every year is how infrastructure lenders actually size debt, and this tool proves the math is exact, not approximate.

How To Use This Model

Reading This Tool

Enter a project's construction cost and financing mix, then its operating cash flow profile, and this tool sizes senior debt the way an infrastructure lender actually does: sculpting repayment to hold a constant target coverage ratio every single year, not a level amortization schedule.

It then compares that CFADS-supportable debt capacity against whatever debt was actually drawn during construction, the single most important reconciliation in project finance, and whether the gap is a cushion or a balloon determines whether the deal closes as structured.

Construction Phase

Operating Phase

Debt Sizing & Reserves

Tax

Debt service is sculpted so CFADS ÷ Debt Service equals the target DSCR in every year of the debt tenor, this is what actually determines the debt an infrastructure lender will underwrite, not a level repayment schedule.

Construction Financing & Debt Capacity

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Debt Drawn At COD (Incl. Capitalized Interest)

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Capitalized Interest During Construction

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Max CFADS-Supportable Debt (Dmax)

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Sizing Gap (Dmax − Debt At COD)

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Total Project Cost Funding Bridge

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Operating Cash Flow Summary

Year 1 CFADS

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Cumulative Equity Distributions

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Minimum DSCR Achieved

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Distribution Lock-Up Years

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Year 5 Cash Flow Waterfall (Representative Operating Year)

DSCR Over Time vs. Target & Covenant Minimum

Senior Debt Balance & DSRA Balance Over Time

Senior Debt BalanceDSRA Balance

Full Operating Cash Flow & Debt Schedule

Equity Returns

Total Equity Invested

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Total Equity Distributions

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Equity Multiple (MOIC)

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Equity IRR

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Equity Cash Flow Profile (Construction Draws & Operating Distributions)

Sensitivity Of Equity IRR To Key Assumptions

Why Sculpted Debt Beats Level Amortization For The Sponsor

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Reading The Sizing Gap

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What The DSRA Is Actually Protecting Against

The Debt Service Reserve Account exists purely for timing risk, a bad quarter that temporarily depresses cash flow shouldn't automatically trigger default if the underlying project economics are still sound over the full tenor. It's a liquidity buffer, not a loss-absorption buffer, which is exactly why it sits ahead of equity distributions but doesn't change how much debt the project can support in aggregate.

Why The Equity IRR Is So Sensitive To The Construction Period

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Project & Infrastructure Finance

The Core Formulas

Debt Servicet = CFADSt / Target DSCR
Dmax = Σt=1..tenor Debt Servicet / (1+r)t (closed-form debt capacity at the senior rate r)
Balancet = Balancet−1·(1+r) − Debt Servicet (sculpted amortization)
Equity IRR solves: Σt EquityCashFlowt / (1+IRR)t = 0

The debt capacity formula is not an approximation, it's an algebraic identity: a loan balance is always exactly the present value of its own remaining scheduled payments, discounted at its own interest rate. Sculpting to a constant target DSCR fixes the debt service stream independent of the loan size, which is what makes this closed-form solvable directly rather than requiring a circular iteration.

When To Actually Use This Model

  • Teaching project finance debt sizing, DSCR sculpting, and reserve account mechanics in an infrastructure or project finance course.
  • Sanity-checking a lender's or advisor's proposed debt quantum against a project's own CFADS profile before a term sheet is signed.
  • Illustrating why sponsors prefer debt sized to a coverage ratio over a level amortization schedule, since it maximizes proceeds against a growing but uncertain revenue stream.

Key Assumptions & Limitations

  • Uses beginning-of-period balances for interest during the operating phase to keep the debt sizing closed-form and circularity-free, real deals often use average or actual-day-count balances, which requires an iterative solve instead.
  • Ignores subordinate debt, interest rate hedging (many project finance deals swap floating funding to fixed), and a residual/terminal value at the end of the concession.
  • Assumes even, straight-line CapEx drawdown during construction and a single blended senior debt tranche, real deals often have multiple tranches with different tenors and step-up margins.

Foundational References

Yescombe, E. R. Principles of Project Finance. Academic Press.

Fabozzi, F. J., & de Nahlik, C. Project Finance. Euromoney Institutional Investor.

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