Short answer: Bathroom remodel cost depends mainly on the size and layout of the room, the surfaces and details you choose, and how much needs to change behind the walls. Comparing quotes by what's included is more useful than comparing totals.
Size and layout
A larger bathroom takes more surface and more time. Moving fixtures or changing the layout usually costs more than keeping the existing arrangement, so decide early whether the layout itself is the problem.
Surfaces and style
The collection and surfaces you choose are one of the biggest levers. A calm, tile-inspired classic look, a pattern-forward modern look and a large-format stone-inspired luxe look each come with different material and installation considerations.
Details and fixtures
Fixtures, glass, lighting and finishing details add up. Spa-level details are often what turn a nice bathroom into a special one, so it's worth deciding where you want to invest and where you don't.
What's behind the walls
The condition of existing plumbing, framing and moisture protection can change the scope once walls are opened. Older homes in particular may need more than the surface suggests. A thorough in-person assessment up front reduces surprises.
Scope and who does the work
Two quotes can look very different because they include different things. Ask exactly what is and isn't included, who manages the project, and who you can call with a question.
How to compare quotes
Compare scope first, then total. A lower number that leaves out important work isn't actually lower. The right remodeler will explain their quote clearly and answer questions without pressure.