Bathrooms concentrate more regulated systems into less space than any other room, which is why small rooms produce large invoices.
Whether plumbing moves
This is the decision that determines everything downstream.
Replacing fixtures where they already are keeps the project in finish territory — no permits in most jurisdictions, no floor or wall opening for pipework, no structural involvement, and comparatively predictable pricing.
Moving the toilet, bath, shower or basin means new supply and waste runs, which means opening floors or walls, which means permits, inspections and the real possibility of finding something unwelcome. The step up in cost between these two is larger than most homeowners expect.
If you can achieve what you want without moving plumbing, the project becomes dramatically more predictable. It is worth exploring that seriously before assuming a layout change is necessary.
Electrical scope
Modern bathrooms need more circuits than older ones — proper extraction, adequate lighting, heated flooring if specified, and required protection on outlets. In older Washington homes this frequently means new circuits, and occasionally a panel that cannot support them.
Discovered conditions
Opening a bathroom in an older Washington home reliably produces findings. Original wiring. Galvanised supply lines that should be replaced while accessible. Framing damaged by a leak that has been running quietly behind the tiling for years.
None of this is a contractor inventing work. It is what happens when old buildings meet current requirements, and it is why a contingency line belongs in the budget rather than being treated as pessimism.
Ventilation
Inexpensive relative to everything else and disproportionately important in Washington. A correctly sized fan, ducted to terminate outside rather than in an attic, with a short direct run. Getting this wrong produces a mold problem that costs many times what the fan would have.
This is the wrong place to save money, and it is one of the most commonly compromised elements in a bathroom project.
Waterproofing
Also not where to economise. Shower waterproofing is invisible once tiling is complete, and failures announce themselves through damage to something else — a stained ceiling below, a soft floor, a musty smell.
Ask what system is used and how it is detailed at corners, thresholds and where the shower meets the floor. Specific answers indicate a contractor who thinks about it.
Finish level
The most visible variable and the one homeowners control most directly. Tile, fixtures, vanities and fittings span an enormous range at every level, and this is where a budget flexes without changing the underlying scope.
Where budgets slip
Almost always in one of three places: a layout change agreed casually without appreciating the cost step, discovered conditions in an older home, or finish selections drifting upward through a long project. The first two are managed by planning; the third by deciding early and holding to it.