Debt service is the total principal and interest a borrower must pay on a loan over a set period, most often one year. In commercial real estate, annual debt service is the sum of every scheduled principal and interest payment across twelve months. It excludes taxes and insurance, which are counted as operating expenses.
How Is Debt Service Calculated?
Debt service is calculated by adding every scheduled principal and interest payment a loan requires within the period. Per Wall Street Prep, annual debt service equals the sum of principal and interest paid over twelve months, and taxes and insurance are excluded because they sit in operating expenses. For a level-payment loan, multiply the monthly payment by twelve.
The building blocks are the loan amount, the interest rate, and the amortization schedule. On an amortizing loan the monthly payment stays level, but the split between interest and principal shifts over time: early payments are mostly interest, later payments mostly principal. Annual debt service still equals twelve monthly payments regardless of that internal split.
Input | Definition |
Loan amount | The outstanding principal balance on which payments are computed |
Interest rate | The annual rate charged on the principal |
Amortization | The schedule over which principal is repaid, such as 30 years |
Annual debt service | The sum of twelve monthly principal and interest payments |
A useful check: on an interest-only loan, annual debt service equals the loan amount times the interest rate, because no principal is repaid. Once amortization begins, debt service rises above that figure by the amount of principal retired each year.
Why Debt Service Matters
Debt service matters because it is the denominator in the two tests that size most commercial loans: debt service coverage ratio and break-even occupancy. Per J.P. Morgan and Wall Street Prep, lenders divide net operating income by annual debt service to get DSCR, so a higher debt service directly lowers coverage and can shrink the loan a property supports.
For an operator, debt service is the fixed claim that stands ahead of equity every month. If net operating income falls but debt service does not, the cushion between them narrows and the risk of default rises. This is why a rise in interest rates or a shorter amortization, both of which raise debt service, can turn a comfortable deal into a tight one without any change in the property itself.
Example
A $10,000,000 loan carries a 6% fixed interest rate and a 30-year amortization schedule. The level monthly payment is $59,955, computed from the standard amortization formula. Multiply by twelve to get annual debt service of $719,461. That figure is what the property must cover from income before any cash reaches equity.
Step | Calculation | Result |
Loan amount | Given | $10,000,000 |
Rate and amortization | Given | 6% over 30 years |
Monthly payment | Amortization formula | $59,955 |
Annual debt service | $59,955 x 12 | $719,461 |
Now test coverage. If the property produces $900,000 of net operating income, DSCR equals $900,000 divided by $719,461, or 1.25x. If the same loan were interest-only, annual debt service would be $10,000,000 times 6%, or $600,000, and DSCR would rise to 1.50x. The only variable that changed was whether principal was being repaid.
Variations and Edge Cases
Debt service is straightforward on a fixed, fully amortizing loan, but several structures change the figure an underwriter should use. The table below covers the common variants.
Variant | Effect on debt service |
Interest-only period | Debt service equals loan times rate; lower until amortization begins |
Floating rate | Debt service rises and falls with the index; underwrite to a stressed rate |
Balloon or bullet | Small periodic payments, then a large principal repayment at maturity |
Constant amortization | Principal is level and interest declines, so payments fall over time |
Debt service including reserves | Some lenders add required reserves; confirm the definition in the loan agreement |
The most common mistake is comparing DSCR across deals without checking whether each debt service figure includes principal. An interest-only loan and an amortizing loan of the same size and rate produce different debt service and therefore different coverage, even though the property is identical.
Debt Service vs Debt Service Coverage Ratio
Debt service is often confused with debt service coverage ratio, but one is a dollar amount and the other is a ratio. Debt service is the annual principal and interest owed, expressed in dollars such as $719,461. Debt service coverage ratio is net operating income divided by that debt service, expressed as a multiple such as 1.25x.
The practical link is direct: debt service is the denominator of DSCR. Raise debt service, through a higher rate or faster amortization, and DSCR falls even if income is flat. Lenders quote a minimum DSCR, but they enforce it by controlling the debt service through loan size, rate, and term.
Frequently Asked Questions
What is included in debt service?Debt service includes the principal and interest payments on a loan for the period. It excludes property taxes and insurance, which are treated as operating expenses, not debt service. Annual debt service is the sum of twelve monthly principal and interest payments.
How do you calculate annual debt service?Annual debt service is calculated by summing the principal and interest payments over twelve months. For a level-payment loan, multiply the monthly payment by twelve. A $10,000,000 loan at 6% over 30 years has a monthly payment of about $59,955 and annual debt service of about $719,461.
Does debt service include principal or just interest?Debt service includes both principal and interest on an amortizing loan. On an interest-only loan, debt service equals the loan amount times the interest rate, because no principal is repaid during the interest-only period.
Related Terms
Net Operating Income
Debt Service Coverage Ratio
Amortization
Debt Yield
Break-Even Occupancy