Multi-unit properties demand a different level of financial scrutiny than single-family investments. Most agents can recite gross rental income; fewer can walk an investor through actual operating expense ratios, defensible vacancy assumptions, and the cap rate math that determines whether a fourplex at $1.2M pencils out or bleeds cash. Your job isn't to replace the investor's accountant or property manager—it's to present the numbers cleanly enough that they can make an informed offer or walk away before due diligence costs pile up.

This article breaks down the three core metrics you need to discuss intelligently with any client eyeing multi-unit income property: operating expenses as a percentage of gross income, realistic vacancy and collection loss, and cap rate calculation with local context. We'll use Ontario and Alberta examples where regulatory or market conditions differ, and flag the line items that sellers love to hide.

Operating Expenses: The 50% Rule and Where It Breaks Down

The 50% rule—operating expenses consume roughly half of gross rental income—is a useful starting point for small multi-units (duplex to sixplex). It excludes debt service but includes property tax, insurance, maintenance, utilities (if landlord-paid), property management, and reserves for capital expenditure. In Toronto, a fourplex grossing $120,000 annually might see $55,000 to $65,000 in opex, depending on age and whether tenants pay utilities. In Calgary, lower property tax rates and cheaper insurance can push that ratio closer to 45%, but deferred maintenance on older wood-frame walkups eats the savings.

The rule fails in two directions. Newer builds with minimal repair needs and tenant-paid utilities can run at 35–40% opex. Conversely, older buildings with oil heat, landlord-paid water, and a neglected roof can hit 60%. Your role is to obtain the actual operating statement—preferably two years—and line-item the expenses:

Property tax: Verify the assessment and any pending appeals. A re-assessment can swing annual tax by $3,000–$8,000 on a small multi.
Insurance: Call a commercial broker for a quote. Stated premiums are often stale or exclude flood/sewer backup riders now standard in Ontario.
Utilities: If landlord-paid, get 12 months of bills. Sellers average winter and summer; you want the peak.
Repairs and maintenance: Anything under 5% of gross income is fantasy. Budget 8–12% for buildings over 20 years old.
Management: Even if the investor plans to self-manage, impute 8–10% of gross rent. Their time has value, and future buyers will underwrite a fee.
Capital reserves: $250–$400 per unit per year minimum. Roof, HVAC, and parking resurfacing aren't operating expenses until they fail.

Walk the property with the investor. Deferred maintenance—cracked asphalt, rusted eavestroughs, 20-year shingles at year 18—turns into capital calls within 24 months. Adjust the opex forecast accordingly and document your assumptions in writing.

Vacancy and Collection Loss: Regional Realities and Lease Rollover Risk

Sellers present rent rolls at 100% occupancy. Your investor needs a vacancy and collection loss assumption between 5% and 10% of gross potential income, depending on market, tenant quality, and lease structure. In a tight rental market—Toronto's pre-construction condo belt, for example—a well-maintained fourplex with long-term tenants might justify 3–5%. In Calgary or Edmonton, where vacancy rates have touched 6–8% in recent cycles, use 8–10% unless the building has a waitlist you can verify.

Collection loss is separate from physical vacancy. Rent control jurisdictions (Ontario's pre-November 2018 units) create tenants who stay but sometimes defer payment, knowing eviction through the Landlord and Tenant Board takes four to six months. Budget 2–3% for collection lag and legal costs even in strong markets. Alberta's faster eviction process reduces this to 1–2%, but higher turnover offsets the gain.

Lease rollover risk matters more than most agents acknowledge. A triplex with all leases expiring in the same quarter creates three months of potential vacancy if tenants don't renew. Stagger lease ends when possible, and if the building is subject to rent control, calculate the gap between in-place rents and market rents. A building with tenants paying $1,400 when market is $1,900 looks like a value-add opportunity until you realize Ontario's 2.5% annual guideline means it takes eight years to close that gap—if the tenants stay.

Cap Rate Calculation: Net Operating Income and the Market Reality Check

Cap rate is net operating income divided by purchase price (or current value). It's the unlevered return—what the property yields before mortgage payments. A duplex generating $48,000 gross income, $26,000 in operating expenses, and $22,000 NOI purchased at $550,000 has a 4% cap rate. That's defensible in Toronto's low-rise market; it's a money pit in London, Ontario, where 6–7% caps are normal.

Calculate cap rate using stabilized NOI, not the seller's inflated pro forma. Stabilized means market rents (not aspirational rents), realistic vacancy, and actual operating expenses including reserves. If the seller claims $30,000 NOI but you've identified $4,000 in deferred maintenance annually and $2,000 in understated insurance, your stabilized NOI is $24,000. At $550,000, that's a 4.36% cap, not the 5.45% the listing advertised.

Compare your calculated cap rate to recent sales of similar vintage, unit count, and location. TRREB, CREA, and local boards publish some multifamily data; commercial brokerages (CBRE, Colliers, Avison Young) release quarterly reports with cap rate ranges by asset class and region. In Q3 2026, expect:

GTA small multi-units: 3.5–4.5% (rent-controlled stock), 4.5–5.5% (post-2018 builds)
Greater Vancouver: 3.0–4.0% (land value dominates)
Calgary/Edmonton: 5.5–7.0% (higher yields, higher vacancy risk)
Ottawa, Hamilton, Kitchener-Waterloo: 4.5–6.0% (depends on proximity to employment nodes)

A property trading 100–150 basis points below market cap rate signals either a unique attribute (new build, prime location, long-term leases) or a pricing error. A property 100+ basis points above market cap suggests distress, deferred capital expenditure, or a seller testing the market. Your investor should know which scenario applies before they write an offer.

Debt Service Coverage and the CMHC Lens

If your investor is financing through CMHC-insured multi-unit lending, the underwriter will calculate debt service coverage ratio: NOI divided by annual debt service. CMHC typically requires 1.15–1.25 DSCR depending on the program. A property with $24,000 NOI can support roughly $19,200–$20,870 in annual debt payments (mortgage principal and interest). At 5.5% on a 25-year amortization, that's a mortgage of about $290,000–$315,000, meaning the investor needs $235,000–$260,000 down on a $550,000 purchase.

Conventional lenders (non-insured) often require 1.20–1.30 DSCR and use their own expense assumptions, which may be more conservative than the seller's figures. Walk your investor through a sensitivity table: if interest rates rise 50 basis points or opex increases 10%, does the deal still clear the lender's DSCR threshold? If not, the investor either increases the down payment or walks.

OSFI's B-20 stress test applies to rental property financing. The borrower must qualify at the contract rate plus 2% or the Bank of Canada five-year benchmark, whichever is higher. A 5.5% mortgage gets stress-tested at 7.5%. Many investors who could service the actual debt fail the stress test, forcing larger down payments or alternative lenders at higher rates. Know the investor's credit profile and down payment capacity before you show properties at the top of their stated budget.

Presenting the Analysis: Spreadsheet Discipline and Professional Boundaries

Deliver your operating expense and cap rate analysis in a simple spreadsheet: one tab for the seller's figures, one tab for your adjusted figures, one tab for sensitivity scenarios (±10% rent, ±10% opex, +50bps interest rate). Include footnotes for every assumption. State clearly in writing that you are not providing financial or investment advice, that the investor should verify all figures independently, and that they must consult their accountant and lawyer before firming an offer.

This protects you from liability and sets the expectation that you're providing data, not recommendations. Some investors will ignore your conservative assumptions and chase yield anyway. Let them—your job is to present the math, not to parent their risk tolerance. Others will appreciate the rigor and return when they're ready to buy a building that actually cash-flows.

Master these three metrics—operating expenses as a percentage of gross income, vacancy assumptions tied to local market conditions, and cap rate calculated from stabilized NOI—and you'll separate yourself from agents who forward listing sheets and call it investor service. The investors who build portfolios work with agents who can read a rent roll, challenge a pro forma, and explain why a 4% cap in one neighborhood is a bargain and a 6% cap in another is a trap. Be that agent, document your work, and let the numbers do the selling.