Commercial mortgage math
DSCR is a cash-flow coverage test, not just a ratio
DSCR asks whether the property's normalized income can cover its mortgage payments. The division is easy; the real underwriting work is deciding what NOI and debt service belong in the calculation and how much safety margin the lender requires.
DSCR compares normalized property income with annual debt payments
Debt-service coverage ratio (DSCR) = normalized net operating income (NOI) ÷ annual debt service. A DSCR of 1.00× means the qualifying property income equals the annual mortgage payments. A ratio above 1.00× leaves a cash-flow cushion; below 1.00× means the qualifying property income does not cover the modelled debt service.
The division itself is easy; the underwriting judgment sits in the inputs. Before trusting the ratio, establish a normalized NOI and model the annual principal-and-interest payments the lender will actually test. Use the NOI Calculator for the numerator and the DSCR Calculator immediately afterward for the coverage ratio.
Calculate NOI before calculating DSCR
DSCR can look precise while being wrong if the NOI is wrong. A lender may normalize rent, vacancy, management, repairs, property taxes, insurance and other operating expenses rather than simply accepting the seller's or borrower's reported number.
The safest workflow is therefore gross property income → normalized operating expenses → normalized NOI → annual debt service → DSCR. Use the NOI Calculator before the DSCR calculator when the NOI itself is uncertain.
The numerator and denominator must describe the same period and the same financing scenario
Do not divide annual NOI by one monthly mortgage payment. Either annualize both sides or use a consistent monthly model. In commercial underwriting, an annual presentation is usually easiest to audit because leases, operating statements and debt service can all be reconciled to the same twelve-month period.
Also decide which debt service is being tested. A property-level first mortgage, subordinate debt, seller financing or other required payments can change the true coverage picture even when a simple calculator shows a comfortable first-mortgage DSCR.
HopeWell's practical sequence is normalize NOI → model the exact financing payments → annualize consistently → calculate DSCR → stress both sides. The DSCR Calculator is most useful after those inputs are settled, not before.
Worked example: $250,000 NOI and $200,000 annual debt service
Suppose a property produces $250,000 of normalized annual NOI and the proposed mortgage requires $200,000 of annual principal and interest. DSCR is $250,000 ÷ $200,000 = 1.25×.
That does not mean the lender has a 25% profit margin. It means the qualifying NOI is 1.25 times the modelled annual debt service. The amount of real-world cushion depends on whether the NOI assumptions remain true.
| Input | Amount |
|---|---|
| Normalized NOI | $250,000 |
| Annual debt service | $200,000 |
| DSCR | 1.25× |
There is no single universal commercial DSCR minimum
Commercial lenders set coverage requirements according to property type, risk, leverage, amortization, sponsor strength and program. A commonly discussed threshold such as 1.20× or 1.25× should never be presented as a universal Canadian rule.
A useful example of why context matters is CMHC MLI Select: its published minimum debt-coverage requirements vary by use, including 1.10× for standard rental residential space, 1.20× for certain other shelter models and 1.40× for non-residential space. Those are program-specific requirements—not general commercial-lender DSCR rules.
DSCR can be solved backwards to estimate maximum annual debt service
If normalized NOI is known and a lender requires a particular DSCR, rearrange the formula: maximum annual debt service = NOI ÷ required DSCR.
At $250,000 NOI and a 1.25× requirement, maximum annual debt service is $200,000. But that is not yet the maximum mortgage. The supported loan amount still depends on the qualifying interest rate, amortization and payment structure. Use the Commercial Mortgage Calculator to translate annual debt service into financing.
Stress the NOI and financing terms because DSCR can move quickly
Using the same $200,000 annual debt service, a 10% decline in NOI reduces $250,000 to $225,000 and DSCR from 1.25× to 1.125×. A lender looking only at the initial ratio would miss how thin the cushion becomes under modest operating stress.
Rates and amortization matter from the other direction. Higher qualifying rates or shorter amortization increase annual debt service and reduce DSCR even when the property NOI is unchanged.
| Scenario | NOI | Annual debt service | DSCR |
|---|---|---|---|
| Base | $250,000 | $200,000 | 1.25× |
| NOI falls 10% | $225,000 | $200,000 | 1.125× |
| Debt service rises 10% | $250,000 | $220,000 | 1.136× |
A passing DSCR does not prove the mortgage works
DSCR answers one question: whether qualifying cash flow covers qualifying debt service with the required margin. It does not establish property value, environmental acceptability, lease quality, borrower liquidity, guarantor strength, title quality or marketability.
A commercial file should therefore be read through several lenses at once: DSCR, debt yield, LTV, property value and the financial strength of the borrower or guarantor.
A disciplined DSCR decision sequence prevents false precision
- Verify and normalize the property's income and expenses.
- Calculate NOI without financing costs.
- Model annual debt service at the lender's proposed or qualifying terms.
- Calculate base DSCR and compare it with the actual program requirement.
- Recalculate under lower rent, higher vacancy, higher expenses or different financing terms.
- Test debt yield, LTV and sponsor strength rather than treating DSCR as the whole credit decision.
- Use DSCR Calculator and NOI Calculator to reproduce the math.
Sources and methodology
Sources and verification
Commercial DSCR requirements vary by lender, property type and program. The page therefore separates the mathematical relationship from program-specific examples and lender underwriting judgment.