Lenders typically apply an offset to that rental income rather than counting it dollar for dollar, since vacancy and maintenance risk on a rental unit are real costs the lender wants covered before it counts toward your qualifying income.
A signed lease with an established tenant is treated more favourably than a projected rent for a unit that has never been leased, so documentation matters as much as the number itself when a lender underwrites the file.
The debt service ratios that decide your maximum mortgage still count property taxes, heating and other debts alongside whatever rental income is allowed, generally capped around 39 percent of gross income for housing costs and 44 percent for total debt under CMHC guidelines, so a full pre-approval with your actual numbers beats a rough estimate. Get your hand-reviewed valuation from Joel Dyck.