To calculate the maximum loan amount using DSCR, divide the property’s net operating income by the lender’s required debt service coverage ratio to get the maximum annual debt service, then convert that annual payment into a loan principal using the interest rate and amortization schedule. A property with $250,000 in net operating income and a lender requiring a 1.25 DSCR can support $200,000 in annual debt service ($250,000 ÷ 1.25). At a 7% rate on a 30-year amortization, that $200,000 supports roughly $2,506,000 in loan principal. The math itself is quick. The work is in getting each input right, because a small error in NOI or a misread on the rate quote can swing the final number by hundreds of thousands of dollars.
The Four Inputs You Need
Four variables drive the entire calculation, and you need all four before you open a spreadsheet.
Net operating income. You’ll calculate this yourself from the property’s financials. It’s the input most likely to be wrong, and it gets its own section below.
The lender’s minimum DSCR. Most lenders require at least 1.20 for stabilized multifamily properties. Riskier property types like hotels or single-tenant retail often face requirements of 1.30 to 1.50. Your lender’s term sheet will spell out the exact figure.
The interest rate. Commercial loans are typically quoted as a spread over a benchmark rate, usually SOFR for floating-rate loans or the 10-Year Treasury for fixed-rate deals. What matters for the calculation is the fully loaded rate you’ll actually pay. Some lenders also include an interest rate floor that sets a minimum rate regardless of how low the benchmark drops. If the floor is higher than the current market rate, use the floor, because that’s the rate the lender will underwrite to.
The amortization period. Most commercial loans use a 25- or 30-year amortization even when the loan itself matures in 5, 7, or 10 years. A longer amortization reduces the annual payment and increases the loan the property can support. The term sheet will specify which schedule applies.
Calculating Net Operating Income the Way a Lender Will
NOI is where the calculation lives or dies. Get this wrong and every number downstream is fiction.
Start with gross potential income: the total rent the property would collect if every unit were occupied at market rates for the full year, plus ancillary revenue from parking, storage, laundry, or other sources.
Vacancy and Credit Loss
No property stays fully occupied with every tenant paying on time. Lenders apply a vacancy and credit loss factor to gross potential income before doing anything else. Even if the building is fully leased today, most underwriters deduct at least 5% for physical vacancy and additional credit loss. If the submarket has historically run at higher vacancy, expect the lender to use the higher figure. What you have left is effective gross income, the realistic revenue figure the lender will work from.
Operating Expenses
Subtract all recurring operating expenses from effective gross income. The major line items are property taxes, insurance, utilities for common areas, landscaping and maintenance, and property management fees. Third-party management typically runs between 4% and 10% of effective gross income, with smaller and more hands-on properties at the higher end.
Lenders verify these figures against historical financial statements, usually the trailing 12 months plus at least one prior year, and cross-reference against federal tax returns or the Schedule E filing that reports rental income and expenses.
What to Leave Out
NOI reflects the property’s ongoing cash-generating ability, so several categories of spending are deliberately excluded. Do not subtract mortgage payments, loan interest, depreciation, income taxes, or one-time capital expenditures like a roof replacement. Depreciation is a paper deduction with no cash leaving the building. Debt service is what you’re sizing to, not an input. Capital expenditures are handled separately through reserves.
The Replacement Reserve Wrinkle
Many lenders deduct an annual replacement reserve from NOI before running the DSCR, even if the property doesn’t currently set that money aside. The reserve covers eventual big-ticket work like roofing, HVAC, and parking lot resurfacing. HUD-backed multifamily loans require a minimum of $250 per unit per year. Conventional lenders vary, but most use a similar per-unit figure or a percentage of effective gross income. If your lender takes reserves above the line, your effective NOI drops and so does the maximum loan. Ask where reserves sit in the underwriting model, because the answer can move the final number materially.
Step 1: Find the Maximum Annual Debt Service
This is the simplest math in the process and carries the most weight. Divide NOI by the lender’s required DSCR.
With $250,000 in NOI and a 1.25 required DSCR, the maximum annual debt service is $200,000. That figure is the ceiling on combined principal and interest payments over 12 months. The lender will not approve a loan whose annual payments exceed it.
The 1.25 ratio means the property earns 25% more than it owes on the mortgage each year. That cushion absorbs rent declines, tax increases, or a spike in vacancy without pushing the property into default. If your NOI is borderline, an increase in the required ratio from 1.25 to 1.30 can cut the maximum loan by tens of thousands of dollars.
Step 2: Convert Annual Debt Service Into a Loan Amount
You now know the most the property can pay each year. The next step is figuring out how large a loan that payment can service at your specific interest rate and amortization. The tool is the mortgage constant, sometimes called the loan constant.
The Mortgage Constant
The mortgage constant is annual debt service expressed as a percentage of the total loan amount. It rolls the interest rate and amortization schedule into a single number. A lower constant means each dollar of annual payment supports a larger loan. Longer amortization and lower interest rates both push the constant down and the maximum loan up.
The formula uses the monthly interest rate (annual rate divided by 12) and the total number of monthly payments (amortization in years multiplied by 12). Most people use a spreadsheet’s PMT function or a financial calculator rather than computing it by hand.
Running the Numbers
Take the running example: $200,000 in maximum annual debt service, a 7% interest rate, and a 30-year amortization. At those terms, the annual mortgage constant is roughly 7.98%. Divide the debt service by the constant:
$200,000 ÷ 0.0798 = approximately $2,506,000
That figure is the largest loan principal the property can support on cash flow alone. Every variable moves it. At a 6% rate the constant drops to about 7.20%, and the same $200,000 supports roughly $2,778,000 in principal. Shorten the amortization to 25 years at 7% and the constant rises to about 8.48%, cutting the maximum to roughly $2,358,000. Plug in your actual rate and amortization to get a number you can rely on.
The Spreadsheet Shortcut
In Excel or Google Sheets, you can skip the mortgage constant and calculate the loan amount in one step using the PV function:
=PV(rate/12, amortization_years*12, -max_annual_debt_service/12)
For the example: =PV(0.07/12, 360, -16667) returns approximately $2,506,000.
DSCR Is Rarely the Only Cap
Lenders run the property through at least two or three sizing tests and fund whichever produces the smallest loan. The three usual suspects:
- The DSCR-based maximum described above, driven by cash flow.
- The loan-to-value maximum, a cap based on appraised value, commonly 65% to 80% for commercial deals.
- The debt yield minimum, which is NOI divided by the loan amount, with most lenders requiring at least 8% to 10%. A 10% debt yield requirement on $250,000 in NOI caps the loan at $2,500,000 regardless of what the DSCR math produces.
Which constraint binds depends on market conditions. When rates are low, DSCR tends to be generous and LTV becomes the tighter limit. When rates are high, DSCR usually binds first. Debt yield acts as a backstop preventing either of the other two from producing an unreasonably large loan. If DSCR says $2,506,000 but the appraised value is $3,200,000 and the lender caps LTV at 75%, the LTV maximum is $2,400,000 and that lower figure wins. Run all three tests before you rely on any single number.
Leave Room for the Post-Closing Covenant
Sizing the loan to close is only half the picture. Most commercial loan agreements include ongoing DSCR covenants that require the property to maintain a minimum ratio throughout the life of the loan, not just at origination. If NOI drops because of rising vacancies, unexpected repairs, or a tax reassessment, the ratio can slip below the covenant threshold.
When that happens, lenders have several tools. The most common is a cash sweep or lockbox trigger, where all rental income flows into a lender-controlled account until the ratio recovers. In more severe cases, the lender may accelerate repayment, demand additional collateral, or impose financial penalties. Some loan agreements even allow the lender to terminate outright if the violation persists.
The practical takeaway: don’t size the loan to the absolute maximum the DSCR math allows. Building a cushion above the minimum ratio protects you from tripping a covenant during a rough quarter. Experienced borrowers often target a DSCR 0.05 to 0.10 above the minimum to create breathing room. The calculation gives you a ceiling. The number you actually borrow should sit under it.