When you move from residential to commercial mortgage underwriting, the assessment framework shifts fundamentally. Residential lenders focus on the borrower — their income, credit, and debt ratios. Commercial lenders focus primarily on the property and its ability to generate enough income to service the debt. Net Operating Income (NOI) and the Debt Service Coverage Ratio (DSCR) are the two metrics at the centre of that analysis.
If you are working commercial files, you need to understand these numbers well enough to calculate them, explain them to clients, and know in advance whether a deal will meet lender requirements.
Net Operating Income (NOI): what it is
NOI is the annual income generated by an income-producing property after operating expenses are deducted, but before debt service (mortgage payments) and income taxes are applied.
NOI = Gross Rental Income − Vacancy Allowance − Operating Expenses
Operating expenses include: property taxes, insurance, maintenance and repairs, property management fees, utilities paid by the owner, and a structural reserve allowance. They do NOT include mortgage payments or depreciation.
What counts as an operating expense
This is where agents frequently make errors. The following are operating expenses that reduce NOI:
- Property taxes
- Building insurance
- Property management (typically 4–8% of gross income)
- Repairs and maintenance (often estimated at 2–5% of gross income for stabilized properties)
- Utilities paid by the landlord (heat, water, electricity in common areas)
- Structural reserve (capital expenditure reserve — typically $150–$400 per unit per year for residential investment)
- Landscaping and snow removal
- Accounting and legal costs at the property level
The following are NOT operating expenses and should not be deducted when calculating NOI:
- Mortgage payments (principal or interest)
- Income tax
- Depreciation or amortization
- Capital improvements (renovation costs that increase property value)
Vacancy allowance
Lenders do not use the actual vacancy rate of a building when underwriting. They apply a stabilized vacancy allowance — typically 5% of gross income for residential properties in good markets, and 5–10% for commercial (retail, office, industrial). This accounts for the normal expectation that no property maintains 100% occupancy indefinitely.
6-unit residential rental, $1,800/unit/month = $129,600 gross annual income
Vacancy allowance (5%) = $6,480 | Effective gross income = $123,120
Operating expenses: taxes $8,400 + insurance $3,200 + management $9,850 + maintenance $5,000 + reserve $3,600 = $30,050
NOI = $123,120 − $30,050 = $93,070
Debt Service Coverage Ratio (DSCR)
DSCR measures how many times the property's NOI covers the annual mortgage payments (debt service). It answers the question: does this property generate enough income to comfortably service the loan?
DSCR = NOI ÷ Annual Debt Service
Annual debt service = total principal and interest payments for the year, calculated at the lender's qualifying rate.
A DSCR of 1.0x means the property generates exactly enough income to cover the mortgage payments — zero margin. A DSCR of 1.25x means income exceeds debt service by 25%, which gives the lender a meaningful buffer.
Minimum DSCR requirements
Most conventional commercial lenders in Canada require a minimum DSCR of 1.20x to 1.25x. CMHC-insured multi-family lending typically requires 1.10x–1.20x. Higher-risk properties, smaller markets, or shorter lease terms will push lenders to require 1.30x or higher.
Here is why DSCR matters for sizing the loan:
NOI = $93,070 (from example above)
Lender requires minimum 1.25x DSCR
Maximum allowable annual debt service = $93,070 ÷ 1.25 = $74,456
At 6.5% over 25-year amortization, $74,456 in annual payments supports a mortgage of approximately $924,000
If the appraised value is $1,500,000 and LTV is capped at 75%, the maximum LTV-based loan is $1,125,000 — but the DSCR-limited loan is $924,000. The DSCR is the binding constraint here.
Lenders use the lower of the LTV-based maximum or the DSCR-based maximum. On income-producing properties, DSCR often limits the loan amount before LTV does — especially in markets where cap rates are low relative to interest rates.
How lenders stress-test the DSCR
Commercial lenders do not use the contract rate when calculating DSCR. They apply a qualifying rate that is typically the contract rate plus a stress spread, often 200 basis points. This ensures the property can still service the debt if rates rise at renewal.
Some lenders also stress-test the vacancy assumption, using a higher vacancy rate than the current actual figure — particularly for office and retail where market conditions can shift quickly.
Worked DSCR example: retail strip plaza
Retail strip plaza — 5 tenants, total base rent $180,000/year
Vacancy allowance (8%) = $14,400 | Effective gross income = $165,600
Operating expenses: taxes $22,000 + insurance $8,500 + management $13,248 + maintenance $9,000 + reserve $5,000 = $57,748
NOI = $165,600 − $57,748 = $107,852
Qualifying rate 7.5%, 20-year amortization. Proposed mortgage: $1,200,000
Annual debt service = $1,200,000 × (7.5% / 12 payments, 20-year amort) ≈ $113,760/year
DSCR = $107,852 ÷ $113,760 = 0.95x — this deal does not qualify at this loan amount
To achieve 1.25x: max debt service = $107,852 ÷ 1.25 = $86,282/year → maximum mortgage ≈ $910,000
Understanding NOI and DSCR is essential for anyone working commercial mortgage files. These calculations tell you, before you submit anything, whether a deal makes financial sense at the requested loan amount. Agents who can run these numbers quickly and accurately are far more effective in pre-qualifying commercial files and structuring deals that actually get approved.
Want to go deeper on this?
Our Commercial Mortgage course covers NOI, DSCR, cap rates, deal structuring and underwriting — with real income property files and small class sizes.
See courses