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Debt Service

Glossary Term • Beginner • 2 min read

Audience
Lenders • Model Developers • Auditors
Last Reviewed
July 2026
Updated
Version 1.0

Executive Summary

Debt service is the total periodic payment obligation on a loan facility, comprising interest payable in the period and scheduled principal repayment due in the period. In project finance, debt service is the denominator of the debt service coverage ratio (DSCR). The DSCR measures the ratio of cash available for debt service (CADS) to total debt service, and must exceed the minimum threshold specified in the loan agreement throughout the loan life. Debt service is applied at a defined step in the cash waterfall, after operating costs and before reserve contributions and equity distributions.

Key Takeaways

  • ✓ Debt service is the total periodic payment obligation a borrower owes to its lenders on a loan facility in a given period.
  • ✓ The DSCR is calculated as:
  • ✓ In the project finance cash waterfall, debt service is applied after operating costs and before reserve contributions and equity distributions.
  • ✓ - Interest is typically calculated on the opening balance to avoid circular references - The scheduled repayment in each period may be flat, annuity, or sculpted - In the balloon period, the debt service includes the full balloon repayment, which must be included in the DSCR denominator for that period

Definition

Debt service is the total periodic payment obligation a borrower owes to its lenders on a loan facility in a given period. It comprises two components:

  1. Interest: the cost of the outstanding borrowing for the period, calculated as the outstanding balance multiplied by the applicable interest rate (base rate plus margin) for the period
  2. Scheduled principal repayment: the contractually agreed reduction of the outstanding loan balance due in the period

Total debt service in any period = Interest + Scheduled Principal Repayment

Debt Service in the DSCR Calculation

The DSCR is calculated as:

DSCR = Cash Available for Debt Service (CADS) / Debt Service

The definition of both CADS and Debt Service for DSCR purposes is specified in the loan agreement. Common variations include:

  • Whether DSRA interest income is included in CADS
  • Whether the balloon payment at maturity is included in debt service in the maturity period
  • Whether maintenance reserve contributions are deducted before or after CADS

The financial model must implement the DSCR definition exactly as specified in the loan agreement. A mismatch between the model's DSCR calculation and the contractual definition is a material audit finding.

Debt Service in the Cash Waterfall

In the project finance cash waterfall, debt service is applied after operating costs and before reserve contributions and equity distributions. The full waterfall sequence is:

  1. Operating costs
  2. Senior debt service (interest + scheduled principal) ← debt service step
  3. Reserve account funding
  4. Cash sweep / additional amortisation
  5. Subordinated debt service (if applicable)
  6. Equity distributions (subject to distribution test)

Modelling Considerations

  • Interest is typically calculated on the opening balance to avoid circular references
  • The scheduled repayment in each period may be flat, annuity, or sculpted
  • In the balloon period, the debt service includes the full balloon repayment, which must be included in the DSCR denominator for that period

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Prerequisites

  • DSCR — the primary coverage ratio calculated using debt service as the denominator
  • Cash Waterfall — the payment priority structure in which debt service sits
  • Debt Sculpting — the technique for sizing the principal repayment component
  • Balloon Payment — the residual repayment included in debt service at maturity

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Related Articles

Cash Waterfall

A cash waterfall is the contractually defined priority sequence in which cash generated by a project is allocated to successive payment obligations. In a project finance structure, the cash waterfall determines the order in which operating costs, debt service (interest and principal), reserve contributions, and equity distributions are paid from the project's revenue. Senior obligations are paid first; junior obligations and distributions are paid only after senior obligations are fully satisfied. The DSCR and other coverage covenants are calculated at specific points within the waterfall to determine whether cash can flow to the next level.

Debt Sculpting

Debt sculpting is the project finance modelling technique by which the periodic loan repayment schedule is derived from the project's projected cash flows available for debt service, sized in each period to maintain a minimum debt service coverage ratio (DSCR). Rather than specifying equal principal repayments or equal total debt service payments over the loan life, debt sculpting produces a repayment profile whose shape mirrors the project's cash flow curve: larger repayments in periods of high cash generation, smaller repayments in periods of lower cash flow. The result is a higher achievable debt quantum than flat or annuity amortisation while maintaining covenant compliance throughout the loan life.

Balloon Payment

A balloon payment is a large lump-sum repayment of outstanding loan principal that falls due at or near the maturity of a loan, following a period during which scheduled amortisation payments have been lower than would be required to fully repay the loan by maturity. Balloon payments arise in project finance when the debt sculpting algorithm sizes periodic repayments at the minimum required to satisfy the DSCR covenant, which may not be sufficient to fully repay the facility within the loan term. The balloon represents the residual outstanding balance after all scheduled repayments have been made and must be refinanced or repaid from asset sale proceeds at maturity.
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