How accurate is this estimator?
This tool gives you a planning-level estimate, not a formal quotation. It's built to help you set a realistic budget and walk into a conversation with a contractor already informed, not to promise a final price before anyone has seen the job.
The number you get is based on the details you provide - room size, scope, finish level, location, and so on - matched against typical costs for that kind of project. What it can't account for is anything specific to your actual house: what's behind your walls, the condition of your existing plumbing or electrical, site access, or a foundation issue that only shows up once work starts. Those things move a final price, sometimes significantly, and no questionnaire can catch all of them in advance.
Use this estimate as your starting point, not your final answer. A written quote from a licensed contractor, after they've actually seen the space, is the only way to get a firm number - and that quote is what you should treat as binding, not this one.