Know the Numbers Before You Buy.
A rental property is only a good investment if the math works. Before you write an offer, it pays to understand exactly what the property earns, what it costs to run, and what's left after the mortgage. This is a plain-language walk-through of how to analyze cash flow — and how lenders read the same numbers when they decide what to finance.
The building blocks of cash flow
Every rental analysis is built from the same handful of pieces. Get these right and the rest is arithmetic.
The total rent the property can realistically collect each month at market rates — not the best-case number, but what a comparable unit actually leases for today.
No unit is rented every single day of the year. A prudent analysis sets aside a portion of gross rent to cover turnover, a month between tenants, or a soft rental market.
Municipal taxes are a fixed, recurring cost that doesn't stop when a unit sits empty. Use the actual assessed amount, not an estimate.
Landlord or rental-property insurance typically costs more than a standard homeowner policy because it covers rental risk and often liability.
Any heat, hydro, water or gas the landlord pays rather than the tenant. Whether these are your cost depends on the lease and how the property is metered.
Ongoing upkeep plus a reserve for the bigger-ticket items — roof, furnace, appliances — that eventually need replacing.
For condos and some freehold arrangements, monthly fees are a fixed expense that belongs in the analysis even though they aren't "yours" to spend.
Whether you hire a manager or do it yourself, your time has value. Many investors budget a management cost so the numbers hold up if they hand it off later.
Principal and interest on the financing. This is usually the largest single line — and the one that changes most with your down payment, amortization and rate.
Net cash flow, simply
Strip away the jargon and it comes down to one sentence.
Rent, minus operating expenses, minus financing, equals your monthly cash flow.
Start with the rent you can actually collect (gross rent, less a vacancy allowance). Subtract the operating expenses — taxes, insurance, utilities, maintenance, condo fees, management. Then subtract the mortgage payment. What's left is what the property puts in your pocket, or takes out of it, each month.
When the number is positive, the rent covers the property and hands you a surplus — the property carries itself and contributes to your return from day one. When it's negative, you're topping the property up out of your own income each month. Negative cash flow isn't automatically a deal-breaker — some investors accept it in exchange for appreciation or a strong location — but it has to be a decision you make on purpose, with your eyes open, not a surprise you discover after closing.
The most common mistake is optimism: full rent, no vacancy, and no reserve for repairs. Build the analysis on realistic, conservative numbers and it will hold up when a tenant leaves or the furnace quits.
How lenders read it
Your analysis and the lender's are cousins — same building blocks, a stricter eye. Here's what tends to matter when a lender sizes the financing.
Debt-service coverage (DSCR)
Conceptually, lenders compare the income a property produces against the debt payments it has to carry. The higher the coverage, the more comfortably the rent services the mortgage. Ratios and thresholds vary by lender and product — but the idea is simple: they want the property to more than pay for its own financing.
Why reserves matter
Lenders like to see that you can absorb a vacancy, a repair or a rate change without missing a payment. Cash reserves and overall financial strength reassure them that the plan survives a bad month — and they can make the difference between an approval and a decline.
How rental income is counted
Not all rent counts fully. Lenders apply their own rules to how much of the rental income they'll recognize toward qualifying, and they may want leases or market-rent support to back it up. Two lenders can look at the same property and count its income differently.
Stress considerations
Qualifying is generally tested against more than today's payment — the point is to confirm the deal still works if costs rise or conditions tighten. Building a cushion into your own analysis keeps you on the right side of that test rather than scraping the line.
A quick word on cap rate
You'll hear investors talk about cap rate — capitalization rate. At a high level, it's the property's net operating income divided by its price: the return the building would generate if you owned it outright, before any financing.
Cap rate is a useful way to compare properties on an apples-to-apples basis, because it deliberately excludes the mortgage. That's also its limit — it says nothing about your down payment, your rate or your actual monthly cash flow. Use cap rate to compare opportunities, and use a full cash-flow analysis to understand what a specific deal does for you, with your financing.
Want to test the mortgage side of the math? Our calculators can give you a quick payment estimate to plug into your analysis, so you can see how down payment, amortization and rate move your monthly cash flow. Then bring the numbers to Paul and pressure-test the whole picture together.
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Does the property actually cash flow?
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