Real Estate
How To Calculate Debt Service Coverage
Lenders on income producing property care about one question above all: does the property earn enough to make the payments. Debt service coverage ratio is that question turned into a single number.
Quick Answer
DSCR = NOI / annual debt service
- DSCR
- Debt service coverage ratio, how many times over the income covers the debt
- NOI
- Net operating income, gross rent less vacancy less operating costs
- ADS
- Annual debt service, twelve times the monthly loan payment
Take the property's net operating income for the year and divide it by the twelve monthly loan payments. The example property earns 88,800 of net operating income against 72,922.37 of debt service, giving 1.2177.
What Is Debt Service Coverage?
Debt service coverage ratio compares what a property earns to what it owes. A ratio of one means the income exactly covers the loan payments with nothing left over. Above one means there is slack, below one means the owner has to put in cash each month.
Net operating income is the honest measure of what a property earns. It is gross rent, reduced for vacancy, less the running costs of the building: management, maintenance, insurance, property tax. It deliberately excludes the mortgage, because the mortgage is what the ratio is testing.
The exclusion is the point. Including debt service in the income figure would be circular. NOI is what the building produces before financing, and the ratio asks how comfortably that production covers the financing chosen.
Annual debt service is simply twelve monthly payments on the loan, principal and interest together. On an amortising loan it is fixed for the term, which is why the ratio is stable and therefore useful to a lender.
Lenders typically want 1.20 or 1.25 as a floor, and many will not write a loan below 1.00 at any price. The buffer exists because rents fall, tenants leave and roofs leak, and a property running at 1.05 has no room for any of it.
The ratio can be read as a cushion in percentage terms. A DSCR of 1.2177 means income could fall by about 18 percent before it stopped covering the debt. That is a far more useful sentence than the ratio alone.
Vacancy is where most bad DSCR numbers come from. Underwriting at zero vacancy because the building is currently full is the standard error; the vacancy allowance exists precisely for the months when it is not.
Operating expenses are the other soft spot. Owners routinely understate them, and lenders respond by substituting their own minimum, often a percentage of gross income, regardless of what the owner claims.
The debt yield, net operating income over the loan amount, is the companion measure. It ignores the interest rate entirely, which makes it a useful check when a low rate is flattering a thin deal.
Interest rate changes hit the ratio through the payment. On an adjustable loan a rise in the rate raises debt service immediately while rents are locked by leases, so coverage compresses exactly when the owner has least control.
Because the ratio drives the loan amount, it can be inverted. Given a required coverage and a known income, the largest loan that still clears the hurdle falls straight out of the arithmetic.
For the example used here, 12,000 a month of rent at 5 percent vacancy gives 136,800 of effective gross income. Taking off 48,000 of costs leaves 88,800 of net operating income.
The loan is 900,000 at 6.5 percent over 25 years, which is 6,076.86 a month or 72,922.37 a year. Dividing 88,800 by 72,922.37 gives 1.2177.
That clears a 1.20 hurdle but not a 1.25 one. Pushing the loan down until the ratio reaches 1.25 gives 876,767.95, which is the largest advance that satisfies the stricter lender.
The same arithmetic works for any income producing asset with a scheduled repayment obligation, from a single rental to a portfolio, which is why the ratio appears well outside real estate.
Formula
NOI = rent x 12 x (1 - vacancy) - operating expenses
Formula page →What the property earns in a year before any financing cost.
| Symbol | Meaning | Unit | Notes |
|---|---|---|---|
| NOI | Net operating income | currency per year | Annual income less annual operating costs. |
| R | Monthly rent | currency per month | The gross rent collected per month. |
| v | Vacancy rate | fraction | The share of rent expected to be lost to vacancy. |
| E | Operating expenses | currency per year | Running costs for the year. |
ADS = 12 x L x i / (1 - (1 + i)^-N)
Formula page →Twelve monthly payments on a level amortising loan.
| Symbol | Meaning | Unit | Notes |
|---|---|---|---|
| ADS | Annual debt service | currency per year | Total principal and interest paid in a year. |
| L | Loan amount | currency | The principal advanced. |
| i | Period rate | fraction per month | The annual rate divided by twelve. |
| N | Term | months | The number of monthly payments. |
DSCR = NOI / ADS
Formula page →How many times over the income covers the debt.
| Symbol | Meaning | Unit | Notes |
|---|---|---|---|
| DSCR | Coverage ratio | times | A value of 1 means income exactly covers debt. |
| NOI | Net operating income | currency per year | Income before financing. |
| ADS | Annual debt service | currency per year | Debt payments for the year. |
How To Calculate Debt Service Coverage
- 1
Gross up the rent to a year
Multiply the monthly rent by twelve. Twelve thousand a month gives 144,000 of gross annual rent before any allowance for empty months.
- 2
Take out vacancy to get effective gross income
Multiply by one minus the vacancy rate. At 5 percent, 144,000 becomes 136,800. This is the income you should underwrite, not the income a fully let building happens to produce today.
- 3
Subtract operating expenses
Remove management, maintenance, insurance and property tax, but not the mortgage. Costs of 48,000 leave 88,800 of net operating income.
- 4
Work out the annual debt service
Compute the monthly payment on the loan and multiply by twelve. A 900,000 loan at 6.5 percent over 300 months is 6,076.86 a month, so 72,922.37 a year.
- 5
Divide and read the cushion
88,800 divided by 72,922.37 is 1.2177. Invert it to say it plainly: income could drop by roughly 18 percent before it failed to cover the loan.
Examples
Example 1: Small apartment block clearing a 1.20 hurdle
- monthlyRent
- 12000
- vacancyRate
- 5
- operatingExpenses
- 48000
- loanAmount
- 900000
- annualRate
- 6.5
- termMonths
- 300
| Step | Calculation | Result |
|---|---|---|
| Gross annual rent | 12000 x 12 | 144000 |
| Effective gross income at 5 percent vacancy | 144000 x 0.95 | 136800 |
| Net operating income | 136800 - 48000 | 88800 |
| Monthly payment | 900000 x 0.0054167 / (1 - 1.0054167^-300) | 6076.86 |
| Coverage ratio | 88800 / 72922.37 | 1.2177 |
Result: The ratio is 1.2177. The property clears a 1.20 requirement with a thin margin and fails a 1.25 one, which would cap the loan at 876767.95.
Example 2: The same property with a smaller loan
- monthlyRent
- 12000
- vacancyRate
- 5
- operatingExpenses
- 48000
- loanAmount
- 750000
- annualRate
- 6.5
- termMonths
- 300
| Step | Calculation | Result |
|---|---|---|
| Effective gross income | 144000 x 0.95 | 136800 |
| Net operating income | 136800 - 48000 | 88800 |
| Monthly payment | 750000 x 0.0054167 / (1 - 1.0054167^-300) | 5064.05 |
| Coverage ratio | 88800 / 60768.6 | 1.4613 |
Result: Dropping the loan to 750,000 lifts coverage to 1.4613, comfortably above both hurdles, at the cost of a larger equity cheque from the buyer.
Calculator
Debt service coverage ratio
1.2177
- Net operating income
- $88,800.00
- Annual debt service
- $72,922.37
- Debt yield
- 9.87%
- Largest loan at 1.25 coverage
- $876,767.95
Values update as you type. This calculator covers the single scenario its formula assumes — see Common Mistakes for what it leaves out.
Prefer a full-width tool? Open the Debt Service Coverage calculator page.
Common Mistakes
Subtracting the mortgage from income before computing the ratio
Debt service is the denominator, never part of the numerator.
Underwriting at zero vacancy because the building is full today
The vacancy allowance exists for the months when it is not.
Forgetting that operating expenses are annual while rent is often quoted monthly, which throws the scale out by a factor of twelve.
Forgetting that operating expenses are annual while rent is often quoted monthly, which throws the scale out by a factor of twelve.
Using the interest only payment when the loan actually amortises, which understates debt service and flatters the ratio.
Using the interest only payment when the loan actually amortises, which understates debt service and flatters the ratio.
Comparing a ratio computed on one property's actuals against another's pro forma
Underwriting bases differ and the numbers are not comparable.
Assuming a ratio above one means the deal is good
It means the debt is covered; it says nothing about the return on the equity invested.
Ignoring rate resets on adjustable loans
A higher rate raises the denominator immediately while rents are fixed by lease.
FAQ
What DSCR do lenders usually require?
Commercial lenders commonly set a floor between 1.20 and 1.25 for income producing property, and some programmes go higher. Below 1.00 the property does not cover its debt at all and most lenders will not write the loan.
Should the mortgage be included in net operating income?
No. Net operating income is deliberately measured before financing so that the ratio compares income against the financing choice. Putting debt service into the numerator makes the ratio circular.
How is DSCR different from debt yield?
Debt yield is net operating income divided by the loan amount and ignores the interest rate entirely. That makes it a useful cross check when a low rate is making a thin deal look comfortable.
Does a higher ratio always mean a better investment?
No. A very high ratio usually means the loan is small relative to the income, which lowers risk but also lowers the return on the equity invested. It is a lender's measure of safety, not a measure of return.
What is a good vacancy assumption?
It depends on the market and the asset. Lenders frequently substitute their own minimum regardless of the owner's figure, and using recent actual vacancy for the building is a more defensible starting point than zero.
Can the ratio be improved without changing the property?
Yes, by reducing the loan, extending the term or lowering the rate, all of which cut annual debt service. Cutting the loan is the most direct and, as the second example shows, moves the ratio quickly.
References
- [1]Wikipedia, Debt service coverage ratio — https://en.wikipedia.org/wiki/Debt_service_coverage_ratio
- [2]Wikipedia, Net operating income — https://en.wikipedia.org/wiki/Net_operating_income
- [3]Federal Reserve, Commercial real estate finance — https://www.federalreserve.gov/publications/2023-05-19-financial-stability.htm