Start with what your current home would actually sell for, not what an online estimate says, since public records cannot see permitted renovations or a finished secondary suite that a hand review would catch. That gap can be the difference between affording the move and coming up short.
From there, a lender requalifies you at the new price using CMHC's minimum down payment rule, 5 percent to $500,000 and 10 percent above, plus the usual closing costs of 4 to 6 percent for legal fees, adjustments and commission together. Those costs eat into the equity you are counting on to move.
The honest answer is a number, not a feeling, and it starts with what your current house is really worth. Get your hand-reviewed valuation from Joel Dyck.