Let me show you exactly how to calculate debt service coverage ratio—the single most important number in commercial mortgage lending. If you can calculate this yourself, you’ll know whether a deal works before you ever talk to a lender.
This isn’t complicated math. It’s basic division. But understanding what goes into each part of the equation and how to do it correctly—that’s what separates successful investors from those who waste time on deals that won’t qualify.
The Basic DSCR Formula
Here it is. The formula that determines whether you get approved.
DSCR = Net Operating Income / Total Debt Service
That’s it. Take your property’s net operating income for one year. Divide it by the total mortgage payments for one year. The result is your debt service coverage ratio.
A DSCR of 1.25 means your income is 1.25 times your mortgage payment. You’re generating 25% more income than needed to cover the debt. Lenders love cushions, so they love DSCRs above 1.20.
Let me walk you through calculating each component properly.
Step One: Calculate Gross Rental Income
Start with how much rent the property generates in a year. This sounds simple but has nuances.
Add up all the rent your tenants pay. If you have five tenants each paying $2,000 per month, your gross rental income is $120,000 per year ($10,000 per month × 12 months).
Include all rental income from all sources. Office rent, retail rent, apartment rent, parking income, storage income—everything that produces revenue gets counted here.
Use actual, current rent, not potential rent. If a space is vacant, don’t include what you hope to rent it for. Lenders calculate based on money actually coming in, not optimistic projections.
If leases include annual escalations, use the current rent, not future increased rent. Be conservative.
Step Two: Account for Vacancy and Collection Loss
Even if your property is 100% occupied today, lenders assume some vacancy. Tenants leave, spaces sit empty between tenants, some tenants pay late or not at all.
Most lenders use 5% to 10% vacancy and collection loss. If your property type typically runs at 90% occupancy in your market, assume 10% vacancy.
Subtract this from your gross rental income. If your gross rental income is $120,000 and you assume 5% vacancy, your effective gross income is $114,000.
Gross Rental Income: $120,000 Less 5% Vacancy/Collection: -$6,000 Effective Gross Income: $114,000
Some borrowers argue their property will stay 100% occupied forever. Lenders don’t buy it. Build in realistic vacancy assumptions.
Step Three: Calculate Operating Expenses
Now subtract all the costs of operating the property. This gives you net operating income.
Operating expenses include:
Property taxes: Annual property tax bill. This is usually your largest single expense. Get the actual tax amount from the current tax bill, not an estimate.
Insurance: Annual property insurance premium. Get quotes if you’re buying, or use the current policy cost if you own the property.
Utilities: Any utilities you pay as landlord—water, sewer, electricity for common areas, gas for building heat. Don’t include utilities tenants pay directly.
Repairs and maintenance: Annual costs for routine repairs, painting, fixing things that break. Use historical averages if available. If not, estimate 5% to 10% of gross rental income.
Property management: If you hire professional management, include their fee—typically 4% to 10% of gross rent. If you self-manage, lenders sometimes still include a management expense to reflect the true cost.
Landscaping and snow removal: Annual contracts or average costs for these services.
Common area maintenance: Cleaning, lighting, supplies for common areas.
Professional fees: Accounting, legal fees related to property operations.
Capital reserves: Many lenders want to see 3% to 5% of gross income set aside for future capital expenditures like roof replacement or HVAC updates.
What you DON’T include in operating expenses:
- Mortgage payments (those come later in the DSCR calculation)
- Depreciation (it’s an accounting entry, not a cash expense)
- Income taxes (personal expense, not a property operating expense)
- Principal paydown (this is part of debt service, not an operating expense)
Let’s continue our example:
Effective Gross Income: $114,000
Operating Expenses: Property taxes: $18,000 Insurance: $4,000 Utilities: $6,000 Repairs & maintenance: $8,000 Property management (6%): $7,200 Landscaping/snow: $3,000 Common area maintenance: $2,000 Capital reserves (3%): $3,600 Professional fees: $1,200
Total Operating Expenses: $53,000
Step Four: Calculate Net Operating Income
Subtract total operating expenses from effective gross income. This is your NOI—net operating income.
Effective Gross Income: $114,000 Total Operating Expenses: -$53,000 Net Operating Income: $61,000
This $61,000 is what the property actually makes after paying all operating costs but before paying the mortgage. This is the money available to service debt.
NOI is crucial. It’s used for DSCR calculation, property valuation, and investment return analysis. Make sure it’s accurate.
Step Five: Calculate Annual Debt Service
Now figure out your total annual mortgage payments. This includes both principal and interest.
If you’re getting a new mortgage, use the proposed payment. If you’re refinancing, use the new payment, not your current payment.
The easiest way to calculate this is with a mortgage calculator. Input your loan amount, interest rate, and amortization period. It will tell you the monthly payment. Multiply by 12 for annual debt service.
Example: You’re borrowing $400,000 at 6% interest with a 25-year amortization. Using a mortgage calculator, the monthly payment is about $2,577. Annual debt service is $2,577 × 12 = $30,924.
If you have or will have multiple mortgages on the property, add them all together. A $300,000 first mortgage with $24,000 annual payment and a $50,000 second mortgage with $6,000 annual payment totals $30,000 in annual debt service.
Step Six: Calculate DSCR
Now divide your net operating income by your annual debt service.
DSCR = NOI / Annual Debt Service
Using our example:
DSCR = $61,000 / $30,924 = 1.97
A DSCR of 1.97 is excellent. The property generates 97% more income than needed to cover the mortgage. Any lender would be comfortable with this.
What Different DSCR Numbers Mean
Let’s talk about what different results tell you.
DSCR of 1.50 or higher: Excellent. The property generates 50% more income than the mortgage payment. This provides strong cushion against vacancy, expense increases, or other problems. You’ll qualify easily and get the best rates.
DSCR of 1.25 to 1.49: Good. This is the standard range most lenders target. You have adequate cushion and will qualify with most lenders at competitive rates.
DSCR of 1.15 to 1.24: Marginal. You’ll qualify with some lenders, but not all. Expect more scrutiny and possibly slightly higher rates. Some lenders want at least 1.20 or 1.25.
DSCR of 1.05 to 1.14: Weak. The property barely covers its mortgage. Most conventional lenders will pass. Alternative lenders might work with you at higher rates, likely requiring larger down payments.
DSCR below 1.05: The property doesn’t generate enough income to cover its mortgage. You’ll need to either put more money down (reducing the loan and payment), accept a longer amortization (reducing payment), or pass on the deal.
DSCR below 1.00: The property loses money. Hard pass from any conventional lender. Even alternative lenders likely won’t finance unless you have massive down payment or other compelling factors.
Common Calculation Mistakes
Let me save you from errors I see constantly.
Mistake 1: Using gross income instead of net operating income. You can’t divide gross rent by debt service. You need to subtract operating expenses first.
Mistake 2: Forgetting to include all operating expenses. Some borrowers only subtract property tax and insurance, forgetting maintenance, management, utilities, reserves, and other costs. This inflates NOI and gives a misleadingly high DSCR.
Mistake 3: Including mortgage payment in operating expenses, then dividing by debt service. The mortgage payment isn’t an operating expense. It’s the denominator in your DSCR calculation.
Mistake 4: Using monthly NOI but annual debt service, or vice versa. Both numbers need to represent the same time period—either both monthly or both annual.
Mistake 5: Assuming zero vacancy on a fully-occupied property. Lenders will apply a vacancy factor even if the property is currently 100% occupied. Build this into your calculation.
Mistake 6: Using optimistic rent projections instead of current actual rent. Calculate based on what the property generates today, not what you hope it will generate after you improve it.
Working Backwards From Required DSCR
Sometimes it’s useful to work backwards. If you know what DSCR lenders require, you can calculate what mortgage payment you can afford.
Rearrange the formula:
Maximum Annual Debt Service = NOI / Required DSCR
If your property has NOI of $75,000 and lenders require 1.25 DSCR:
Maximum Annual Debt Service = $75,000 / 1.25 = $60,000
So you can afford annual payments of $60,000, or $5,000 per month. Working with a mortgage calculator at 6% and 25-year amortization, this means you can borrow approximately $775,000.
This calculation helps you know what you can afford to pay for properties before you make offers.
Calculating DSCR for Properties You’re Considering
Before you get serious about a property, run the DSCR calculation. Here’s how.
Get the rent roll and operating statements from the seller. Verify the income and expenses are realistic. Calculate NOI.
Determine how much you’d need to borrow. If you’re buying a $1 million property and putting $300,000 down, you need a $700,000 mortgage.
Calculate what that mortgage payment would be at current interest rates. Use realistic rates—check what lenders are currently offering on similar deals.
Divide NOI by the annual mortgage payment. That’s your DSCR.
If it’s above 1.25, you’re probably fine. If it’s below 1.20, you need to think about whether you can make the deal work—maybe with a larger down payment or by finding efficiencies that increase NOI.
How to Improve a Weak DSCR
What if you run the numbers and your DSCR is 1.10—not quite good enough? You have options.
Increase your down payment. Borrow less, which means smaller mortgage payments. If you’re putting 25% down, try 30% or 35%. This reduces the denominator in your DSCR calculation, improving the ratio.
Extend your amortization. A 30-year amortization has lower payments than a 25-year amortization. This reduces debt service, improving DSCR. Not all lenders offer 30-year amortization on commercial properties, but some do.
Increase NOI. Can you raise rents to market rate? Reduce operating expenses? Lease vacant space? Any action that increases NOI improves your DSCR.
Negotiate a lower purchase price. If the DSCR doesn’t work at the asking price, maybe it works at a lower price. You’d borrow less, have lower payments, and better DSCR.
Combine strategies. Maybe you can’t increase down payment enough by itself, but if you combine 30% down payment with a 30-year amortization and modest rent increases, the DSCR works.
DSCR for Different Property Types
Different properties and lenders have different DSCR requirements.
Multi-tenant office and retail buildings with good occupancy usually need 1.20 to 1.25 DSCR. These are well-understood assets with diversified income.
Single-tenant properties often require 1.30 to 1.35 DSCR because all your income depends on one tenant. If they leave, you have zero income until you find a replacement.
Special-purpose properties might need 1.35 to 1.50 DSCR because they’re harder to re-lease if the current use fails.
Apartments often qualify at 1.15 to 1.20 DSCR because lenders view them as lower risk with many small tenants instead of a few large ones.
Know what your property type typically requires and calculate accordingly.
When Lenders Adjust Your DSCR Calculation
Lenders don’t always accept your NOI calculation as-is. They might adjust it.
If you claim zero vacancy but market average is 10%, they’ll apply a 10% vacancy factor. If you say you’ll self-manage but don’t have experience, they might add a management expense.
If some of your rent comes from short-term tenants or month-to-month leases, they might discount that income or not count it at all.
If your property needs major repairs but you haven’t budgeted for them, lenders might add those costs to operating expenses, reducing your NOI.
This is why being conservative in your own calculations is smart. If you calculate a 1.30 DSCR conservatively and the lender adjusts it down slightly, you still have 1.25. If you stretch to calculate 1.25 and they adjust it down, suddenly you’re at 1.15 and you don’t qualify.
Using DSCR to Evaluate Investment Returns
DSCR is a lender metric, but it’s useful for investors too. A higher DSCR means more cash flow cushion, which means safer investment.
A property with 1.50 DSCR has much more margin for error than one with 1.20 DSCR. Vacancies hurt less. Unexpected expenses are more manageable. You sleep better at night.
Aggressive investors sometimes chase maximum leverage and minimum DSCR because it amplifies returns when things go well. Conservative investors prefer higher DSCR for stability.
Neither approach is wrong—it depends on your risk tolerance and investment strategy. But always calculate DSCR so you know what you’re getting into.
Real Example: Running the Full Calculation
Let’s do a complete example from scratch.
You’re buying a small office building for $850,000. You’re putting $250,000 down, borrowing $600,000 at 6.25% with a 25-year amortization.
Step 1: Gross Rental Income Three tenants: $3,500/month, $2,800/month, $2,200/month Total monthly rent: $8,500 Annual gross rent: $8,500 × 12 = $102,000
Step 2: Vacancy/Collection Loss Assume 5% vacancy: $102,000 × 0.05 = $5,100 Effective Gross Income: $102,000 - $5,100 = $96,900
Step 3: Operating Expenses Property taxes: $14,500 Insurance: $3,200 Utilities: $5,000 Repairs & maintenance: $6,000 Property management (6%): $6,120 Landscaping: $2,400 Capital reserves (3%): $3,060 Professional fees: $800 Total: $41,080
Step 4: Net Operating Income $96,900 - $41,080 = $55,820
Step 5: Annual Debt Service $600,000 at 6.25%, 25-year amortization = $3,920/month = $47,040/year
Step 6: DSCR $55,820 / $47,040 = 1.19
This DSCR of 1.19 is just barely adequate. Some lenders require 1.20 minimum. You’d likely qualify, but you’re close to the edge.
To improve to 1.25, you could put down $300,000 instead of $250,000. Borrowing $550,000 would reduce your payment to $3,595/month or $43,140/year. New DSCR: $55,820 / $43,140 = 1.29. Much better.
Your DSCR Calculation Action Plan
Before you get serious about any commercial property, do this calculation. Get the financials from the seller, run the numbers, see what DSCR you get.
If it’s above 1.25, great—move forward. If it’s 1.15 to 1.25, think about whether you can strengthen it. If it’s below 1.15, seriously consider whether the deal makes sense or if you should keep looking.
Don’t wait for lenders to tell you the DSCR doesn’t work. Figure it out yourself first.
At Creek Road Financial Inc., we help clients calculate DSCR and understand what they can qualify for before they start property shopping. We can show you exactly how different down payments, amortizations, and property performance affect your DSCR and approval odds.
DSCR is the gatekeeper to commercial mortgage approval. Master this calculation and you’ll know whether deals work before you waste time on applications that won’t get approved. That’s power.