Welcome to Wall Street Prep! Use code at checkout for 15% off.
Wharton & Wall Street Prep Certificates
Now Enrolling for September 2024 for September 2024
Private EquityReal Estate Investing
Buy-Side InvestingFP&A
Wharton & Wall Street Prep Certificates:
Enrollment for September 2024 is Open
Wall Street Prep

Debt Service

Step-by-Step Guide to Understanding the Annual Debt Service Concept in Real Estate (Principal + Interest)

Last Updated April 16, 2024

Learn Online Now

Debt Service

How to Calculate Debt Service in Real Estate

Debt service in the real estate industry refers to the burden placed on a borrower after committing to a financing arrangement.

The borrower is contractually obligated to service periodic interest and principal payments to the lender once the lending agreement has been formally signed by both parties – including the repayment of the original principal in full at maturity.

From the perspective of commercial lenders, such as banks, debt service is one of the most critical factors to consider when underwriting a loan.

The borrower of a commercial mortgage loan must service its interest and principal payment obligations on time, per the lending agreement.

Otherwise, the borrower is at risk of defaulting on the commercial loan and becoming insolvent. In the event of default, the lender most likely would have the right to seize the property based on the terms as outlined in the original agreement to recoup any monetary losses.

Senior lenders normally require the borrower to pledge the underlying real estate property as collateral to further protect their downside risk (i.e., a lien).

While the borrower is held liable in the event of default, the lender must still actively mitigate risk by performing in-depth diligence on the credit profile of the borrower (and property).

Debt service comprises the periodic principal amortization and interest owed on a loan.

  • Principal → The principal amortization refers to the incremental repayment of the original loan principal.
  • Interest → The interest expense is the cost of financing and reflects the borrower’s perceived credit risk (i.e. higher risk coincides with a higher interest rate, and vice versa).

Real Estate Technical Interview Guide | File Download Form

By submitting this form, you consent to receive email from Wall Street Prep and agree to our terms of use and privacy policy.


Debt Service Formula

The formula to calculate the annual debt service is the sum of the principal payment and interest expense in a specified period.

Annual Debt Service = Principal + Interest

In practice, the annual debt service is most often calculated in Excel, as part of building a loan amortization schedule.

The amortization schedule is a method used to track and calculate the periodic principal amortization and interest owed on a loan, including the outstanding loan principal balance.

The annual debt service can be determined via the built-in PMT function in Excel, which calculates the periodic payment on a loan, inclusive of the interest and principal component.

=PMT(rate, nper, pv, [fv], [type])

The two components of the annual debt obligation — the principal and interest payments — can be separately calculated using the PPMT and IPMT function, respectively.

=PPMT(rate, per, nper, pv, [fv], [type])
=IPMT(rate, per, nper, pv, [fv], [type])

The sum of the principal and interest computed using the PPMT and IPMT function must equal the debt service determined by the PMT function, or else a mistake was likely made.

  • PPMT Function → Principal Payment
  • IPMT Function → Interest Payment
  • PMT Function → Principal Payment + Interest Payment

Maintaining consistency in the units is critical to ensure the accuracy of the payment amounts (i.e. monthly, quarterly, semi-annual, annual).

Note: The PMT, PPMT and IPMT Excel functions each assume a fixed interest rate pricing structure on the loan.

The Wharton Online
and Wall Street Prep Real Estate Investing & Analysis Certificate Program

Level up your real estate investing career. Enrollment is open for the Sep. 9 - Nov. 10 Wharton Certificate Program cohort.

Enroll Today

How to Analyze the Debt Service Ratio

The debt service ratio – more commonly known as the “debt service coverage ratio (DSCR)” – is used by commercial lenders to determine if a property can generate enough income to fulfill its debt obligations.

The debt service ratio is a credit risk underwriting metric that compares the net operating income (NOI) of a rental property to its annual debt service.

The formula to calculate the debt service ratio divides net operating income (NOI) by the annual debt service.

Debt Service Ratio = Net Operating Income (NOI) ÷ Annual Debt Service


  • Net Operating Income (NOI) = (Rental Income + Ancillary Income) – Direct Operating Expenses
  • Annual Debt Service = Principal (P) + Interest (I)

The DSCR is one of the credit metrics relied on in commercial lending to measure the debt capacity and credit risk of a particular borrower.

Lenders often establish parameters on the loan amount based on the insights derived from the DSCR metric, as part of the loan underwriting process.

In the commercial real estate (CRE) market, the standard minimum DSCR is 1.25x. However, the minimum DSCR is conditional on the current macroeconomic environment and state of the credit markets.

  • DSCR = 1.0x → NOI = Annual Debt Service (“Breakeven”)
  • DSCR > 1.0x → NOI > Annual Debt Service (“Sufficient”)
  • DSCR < 1.0x → NOI < Annual Debt Service (“Insufficient”)

By setting a minimum DSCR in the financing arrangement, lenders can ensure the borrower’s cash flow is sufficient to meet the periodic interest and principal repayment obligations.

Debt Service Calculator

We’ll now move on to a modeling exercise, which you can access by filling out the form below.


Get the Excel Template!

By submitting this form, you consent to receive email from Wall Street Prep and agree to our terms of use and privacy policy.


1. Commercial Real Estate Loan Assumptions

Suppose we’re tasked with calculating the debt service of a proposed request for a commercial mortgage to measure the riskiness of partaking in the financing arrangement.

The borrower, a commercial real estate (CRE) investment firm, submitted the following pro forma financial data as part of the application process.

Rental Property – Pro Forma Data Year 1
Gross Potential Rent (GPR) $2,400k
(+) Ancillary Income 200k
Potential Gross Income (PGI) $2,600k
(–) Vacancy and Credit Losses (5.0% of PGI) (130k)
Effective Gross Income (EGI) $2,470k
(–) Direct Operating Expenses (40.0% of EGI) (988k)
Net Operating Income (NOI) $1,482k

The requested 30-year commercial loan amount is $14 million priced at an interest rate of 7.5%.

  • Commercial Loan = $14 million
  • Annual Interest Rate = 7.5%
  • Loan Term = 30 Years

2. Debt Service Calculation Example

Given those set of financing assumptions for the commercial loan, the next step is to insert each figure into the PMT function in Excel.


The annual debt service is approximately $1.2 million, which we’ll confirm by calculating the principal and interest components separately.

  • Annual Debt Service = $1.185 million

The principal payment comes out as $135k, whereas the interest payment is $1,050k.

Combined, the total debt service for Year 1 matches our earlier calculation.

  • Annual Debt Service = $135k + $1.05 million = $1.185 million

Debt Service Calculation Example

3. Debt Service Coverage Ratio (DSCR) Analysis

In the final section of our tutorial, we’ll conclude by calculating the debt service ratio (or DSCR).

The net operating income (NOI) of the commercial property is projected to be $1.482 million while the annual debt service is $1.185 million.

By dividing the property’s NOI by the annual debt service, we arrive at a debt coverage ratio of 1.25x.

  • Debt Service Ratio = $1.483 million ÷ $1.185 million = 1.25x

Debt Service Calculator

Inline Feedbacks
View all comments

The Wall Street Prep Quicklesson Series

7 Free Financial Modeling Lessons

Get instant access to video lessons taught by experienced investment bankers. Learn financial statement modeling, DCF, M&A, LBO, Comps and Excel shortcuts.