Free ADU Cost Calculator
This is the ADU cost calculator I wish homeowners had before they called me. Tell it where you are, what type of ADU you are thinking about, and roughly how big, and it prices the build for your city with a full breakdown, not a national average with a guess on top. It is free, there is no signup, and the estimate shows up the moment you finish. For the numbers behind it, see our ADU cost breakdowns by location and the ADU Wizard Data Hub.
What type of ADU are you planning?
Pick the closest fit. You can change this anytime.
Prices are the low end for a 400 sq ft build in Seattle, so the five compare like for like.
Free ADU cost calculator FAQ
How does this ADU cost calculator work?
You pick your location, the ADU type, the size and a finish level, and it prices the build from the same cost engine that runs the rest of this site. It is not a national average with a multiplier bolted on. It reads your city and works from local construction, permit and fee ranges, then shows the breakdown so you can see where the money goes rather than just a single number.
How accurate is the estimate?
It is a planning-grade estimate, not a bid. I built it to get you into the right range fast, close enough to decide whether an ADU makes sense on your lot before you spend a dollar on a designer. A real bid depends on your soil, your utility connections, your access and a dozen site details no calculator can see, so treat the number as the starting point for those conversations, not the end of them.
Is the ADU calculator free?
Yes, the calculator is free and there is no signup to see your estimate. You answer a few questions and get the full cost breakdown and your local permit timeline on the spot. No account, no sales call attached to getting the number.
What does the cost estimate include?
The breakdown covers the main cost buckets in a real ADU budget: the base construction, site and foundation work, the kitchen and bath, and the soft costs like design and permits. It gives a range rather than a false-precision single figure, because the honest answer at the planning stage is a range. For the deeper numbers behind it, our ADU cost pages walk the same figures by city, size and finish.
Can it tell me what an ADU costs in my city?
Yes. Enter your address or ZIP and the estimate is priced for your city, not a national average, with the permit timeline your local department typically runs. If you want to read the underlying numbers before you run the tool, our cost-by-location pages and the Data Hub carry the ranges the calculator is built on.