The income side depends on whether the rental income is legal and documented. A lender only counts income from a permitted secondary suite toward financing, so an unpermitted basement unit can rent the same as a legal one and still contribute nothing to the return a bank recognizes.
The expense side is where most first-time investors underestimate. Property tax, insurance, a mortgage that compounds semi-annually, and ongoing maintenance all reduce net income before a return calculation means anything, and a 20 percent down payment on a non-owner-occupied purchase changes the cash invested compared to a standard home purchase.
A hand-reviewed look at the specific property, not a neighbourhood average, is what actually tells you the number. Get your hand-reviewed valuation from Joel Dyck.