Why it matters
Two things. The money. A tub and a shower stall occupy roughly the same footprint and drain to roughly the same place. If the new shower sits exactly where the tub sat and the drain does not move, the conversion is essentially part of the tile and waterproofing work you were doing anyway, and it prices inside a normal three-piece refresh. The moment the shower needs a new drain location, or you decide on a curbless or wet-room floor that requires the subfloor to be dropped, you are in a different job: a fixture move is $2,500 to $5,000, and structural floor work is more. The resale trap. If this is the only tub in a family home, think hard before removing it. Buyers with small children filter listings for a bathtub, and a three-bedroom house with no tub anywhere in it narrows your future buyer pool for no gain. Keep a tub somewhere in the house. Convert the ensuite, not the main bath.
How to spot it
A fibreglass one-piece tub-and-surround unit, which has a life of about 20 years and is the default in Canadian homes from roughly 1980 onward; a tub nobody has used in a decade, with a shower curtain still on the rod; a small ensuite where a tub eats the whole room. Count the tubs in the listing photos across all bathrooms before you plan to remove one.
What it costs
We do not have a Canadian source for a standalone tub-to-shower conversion that we are willing to publish, so we will not invent one. What we will tell you is the shape of it: it is priced within a three-piece bathroom refresh if the drain stays where it is, and it steps up by the cost of a fixture move if it does not.
What to do
Monitor. Ask one question: does the drain move? That is the whole cost question. Then ask yourself the resale one: is this the last tub in the house?
Education and triage, not a home inspection. Casaroo can see whether a bathroom has a tub or a shower. Whether the drain can stay put is a plumber's answer, not a photo's. We flag; we don't inspect.