In real estate, debt service is the total principal and interest you pay on a property loan over a given period, usually stated as a monthly or annual figure. For an income-producing property, that single number decides whether the investment earns money or bleeds it. Get the calculation right before you close, and you know whether the deal works. Get it wrong, and you find out the hard way.
What Debt Service Includes
Two components sit at the core. Principal repayment reduces what you originally borrowed. Interest is what the lender charges for the use of that capital. On a standard amortizing loan, both are combined into one fixed monthly payment, but the split shifts over time. Early on, most of the payment goes to interest because the balance is still large. Later, more of each payment chips away at principal.
Your actual monthly obligation usually goes beyond principal and interest. Many lenders require an escrow (or impound) account that collects a share of annual property taxes and insurance premiums with each payment. The servicer holds the funds and pays the bills on your behalf, so you’re not hit with a lump sum once or twice a year.1Consumer Financial Protection Bureau. What Is an Escrow or Impound Account?
Because tax rates and premiums change annually, the escrow portion fluctuates, which means your total outlay can shift even when principal and interest stay fixed. Skip the escrow and fail to pay taxes or insurance yourself, and the lender can add the unpaid amounts to your loan balance or buy force-placed insurance at a much higher cost.1Consumer Financial Protection Bureau. What Is an Escrow or Impound Account?
Replacement Reserves
Commercial loans, especially multifamily deals financed through agency lenders like Fannie Mae or Freddie Mac, often require a separate monthly deposit into a replacement reserve. The money sits in a lender-controlled account and can only be released for approved capital work: roof replacements, HVAC systems, parking lot resurfacing. Agency lenders typically require around $250 to $300 per unit per year, though the exact figure depends on the property’s condition assessment during due diligence. Reserves aren’t debt service in the strict sense, but they’re a mandatory monthly outflow tied to the loan, and skipping them in your underwriting will leave you short.
How Debt Service Is Calculated
On a fixed-rate, fully amortizing loan, the math produces a payment that stays constant for the entire term. Three inputs drive it: the loan amount, the interest rate, and the term length. A standard amortization formula sets a payment that covers each month’s accrued interest while retiring enough principal to zero the balance by maturity. Any mortgage calculator will run it. What matters is understanding that small changes in rate or term produce outsized changes in the payment.
The Loan Constant
A useful shortcut for comparing loans is the loan constant, which expresses annual debt service as a percentage of the loan amount. Borrow $1,000,000 and pay $78,000 a year, and the loan constant is 7.8%. One number captures the combined effect of rate, amortization, and payment frequency, which makes it easy to line up two offers. Lower is better. The constant only works cleanly for fixed-rate loans; on a floating rate, it changes every time the rate resets.
The loan constant also matters for leverage. When a property’s cap rate exceeds the loan constant, the borrowed portion earns more than it costs to service, and your return on equity climbs. When the constant exceeds the cap rate, the opposite happens.
Interest-Only and Balloon Structures
Not every loan fully amortizes. An interest-only loan requires only interest payments for a set period, with no principal reduction. Debt service during that window is lower and near-term cash flow is higher, but the balance doesn’t shrink. When the interest-only period ends, payments jump because the loan starts amortizing the full original balance over a shorter remaining term.
A balloon loan sits between the two. Payments are calculated as if the loan had a long term, often 30 years, but the entire remaining balance comes due after 5, 7, or 10 years. Monthly debt service feels manageable, but a large payoff waits at maturity, usually met by refinancing or selling.
Variable-Rate Loans
Many commercial mortgages carry a floating rate, typically a benchmark plus a fixed spread. SOFR, the Secured Overnight Financing Rate, has replaced LIBOR as the standard benchmark. When the benchmark rises, so does your debt service. When it falls, so do your payments. If you’re underwriting a floating-rate acquisition, stress-testing debt service at several rate scenarios is how you avoid a situation where a rate increase turns a profitable property into a monthly cash drain.
Debt Service Coverage Ratio
The debt service coverage ratio is the number lenders care about most, and it should be the number you care about too. Divide net operating income by annual debt service. NOI is gross income minus operating expenses (management, insurance, property taxes), calculated before debt payments, income taxes, or capital expenditures.
A DSCR of 1.25 means the property generates 25% more income than debt service requires. A ratio of exactly 1.0 means every operating dollar goes to the lender, with nothing left for repairs, vacancy, or your own return. Below 1.0, the property is losing money on an operating basis and you’re covering the shortfall out of pocket.
Most commercial lenders require a minimum DSCR between 1.20 and 1.25, though the threshold varies by property type, loan program, and market. Some investor-focused DSCR programs go as low as 1.0 or slightly below with pricing or leverage adjustments. The required DSCR effectively caps how much you can borrow. If a property produces $125,000 in NOI and the lender wants a 1.25 DSCR, the maximum annual debt service is $100,000, and the loan sizes to that number regardless of what the property appraises for.
Debt Yield
Lenders increasingly use debt yield as a second check. Debt yield equals NOI divided by the total loan amount, expressed as a percentage. Unlike DSCR, it’s independent of the interest rate, amortization schedule, or appraised value. It measures the lender’s return on capital if it had to take back the property tomorrow. Minimums vary by property type but commonly land between 8% and 12%. A property can clear DSCR and still fail the debt yield test, which prompts the lender to reduce the loan or require more equity.
When Debt Costs More Than the Property Earns
Negative leverage happens when the cost of debt exceeds the unlevered return on the property. The cleanest way to spot it is to compare the loan constant to the cap rate. If your loan constant is 7.5% and the cap rate is 6%, every dollar borrowed dilutes your return rather than amplifying it. An all-cash purchase would have produced more.
Negative leverage became widespread during periods of rapidly rising interest rates, when cap rates hadn’t yet adjusted upward. Investors on floating-rate debt watched debt service climb while NOI stayed flat, and some deals slid below a 1.0 DSCR. Once negative leverage takes hold, your returns depend almost entirely on the property appreciating by the time you sell; the operating cash flow alone won’t justify the debt.
Prepayment Penalties and Exit Costs
Debt service isn’t only what you pay while you hold the property. Getting out early has its own price. Commercial lenders build prepayment penalties into loan agreements to protect the income stream they underwrote. Three structures dominate.
- Yield maintenance charges a penalty equal to the present value of the remaining scheduled payments, discounted using the yield on a Treasury security maturing near the loan’s maturity. The penalty is largest early in the term and shrinks as maturity approaches. It’s common on fixed-rate commercial and agency loans.
- Defeasance replaces the property as collateral with a portfolio of government bonds that replicates the remaining payment stream. The loan stays alive on paper; the bonds pay it. Defeasance is standard on CMBS loans and certain Fannie Mae and Freddie Mac multifamily financing. It’s expensive and procedurally complex.
- A step-down penalty is a declining percentage of the outstanding balance. A typical schedule runs 5% in year one, 4% in year two, 3% in year three, and so on, with most lenders waiving the penalty in the last 90 days before maturity. Simpler and more predictable than yield maintenance.
Many commercial loans also include an initial lockout period during which prepayment is prohibited outright. These exit costs belong in your underwriting alongside the monthly payment. A property that looks profitable on a five-year hold can look very different if the prepayment penalty on a ten-year loan eats a large piece of your sale proceeds.
What Happens If You Can’t Pay
Missing debt service triggers default, and the consequences depend on whether the loan is recourse or non-recourse. With a recourse loan, the lender can pursue your personal assets (bank accounts, other real estate, income) if the foreclosure sale doesn’t cover the outstanding debt. The lender can seek a deficiency judgment for the gap between the sale price and the balance owed.
Non-recourse loans limit recovery to the collateral property. Your personal assets stay protected. That protection is rarely absolute, though. Most non-recourse commercial loans include carve-out provisions (sometimes called “bad boy” guarantees) that convert the loan to full recourse if you commit specific acts: fraud, filing unauthorized subordinate liens, misrepresenting financial statements, or failing to pay property taxes and insurance. Trigger a carve-out and you’re personally liable for the full remaining balance, not just the deficiency.
Non-recourse financing is more common on larger commercial loans and generally comes with higher rates or stricter underwriting. Smaller commercial deals and most residential investment loans tend to be full recourse. Knowing which one you signed matters as much as the interest rate.
Tax Treatment
Only part of your debt service is deductible. Principal repayment isn’t; it reduces the loan balance but isn’t an expense for tax purposes. The interest portion is generally deductible as a rental expense on Schedule E.2Internal Revenue Service. Publication 527 (2025), Residential Rental Property
If you use part of a property personally and rent out the rest, you must allocate mortgage interest between the two uses. Only the rental portion goes on Schedule E; the personal portion may be deductible on Schedule A if the property qualifies as a main home or second home.2Internal Revenue Service. Publication 527 (2025), Residential Rental Property
For larger real estate operations treated as a trade or business, interest deductions may be capped by Section 163(j) of the tax code. Under that provision, deductible business interest in a given year generally cannot exceed business interest income plus 30% of adjusted taxable income.3Office of the Law Revision Counsel. 26 USC 163 – Interest Most real estate businesses can elect out by treating themselves as an excepted real property trade or business, but the election forces depreciation under the Alternative Depreciation System (longer recovery periods, no bonus depreciation) and is irrevocable. Run the numbers with a tax advisor before you make the call.4Internal Revenue Service. Questions and Answers About the Limitation on the Deduction for Business Interest Expense
Debt Service and Your Actual Return
What’s left after debt service is your leveraged cash flow, the money you take home. Cash-on-cash return divides that leveraged cash flow by your initial equity. Higher leverage means higher debt service, but also less equity invested, so when the property performs, your percentage return on that smaller base can beat an all-cash purchase by a wide margin.
That amplification runs both ways. A 10% drop in NOI hits an all-cash investor proportionally. The same drop on a highly leveraged property can wipe out cash flow entirely and push the DSCR into dangerous territory. Debt service is fixed; rents and expenses aren’t. Thin DSCR margins leave very little room to absorb bad quarters before you’re writing checks instead of cashing them.
Debt service also shapes valuations indirectly. Cap rates are unlevered, but buyers who need financing price their debt costs into what they’ll pay. When rates rise and debt service gets more expensive, buyers offer less to preserve their cash-on-cash returns, cap rates drift higher, and property values slide. A rate move ripples across the whole market.
The discipline that separates durable real estate investing from the other kind is maintaining positive leveraged cash flow under realistic stress scenarios, not just the rosy assumptions you used to justify the purchase. Run higher vacancy. Run higher expenses. If you’re on a floating rate, run higher interest. If the deal still services its debt in that scenario, the leverage is working for you. If it doesn’t, the debt service will eventually work against you.