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ADU Cost Calculator, California

Early, system-by-system budget for a garage-conversion ADU, a new detached ADU, or an attached room addition. Plans, soils, utilities and city fees move it most.

Typical mid-range budget: $232k–$265k, depending on the city, for a 600 sq ft detached ADU with one bathroom and a full kitchen.

Estimate my ADU or room addition by ZIP Costs by city

Budget estimate, not a bid, appraisal, or insurance claim valuation. Get licensed contractor bids. Pilot.

ADU or room addition cost by California city

Mid finish, same size everywhere. Likely is the median of 4,000 simulated outcomes; the range is the 10th to 90th percentile.

City (ZIP)	Likely	Range
Los Angeles (90026)	$246k	$209k–$288k
San Diego (92104)	$243k	$207k–$284k
San Jose (95112)	$265k	$223k–$314k
San Francisco (94110)	$264k	$223k–$313k
Sacramento (95819)	$238k	$202k–$282k
Fresno (93704)	$232k	$196k–$275k
Riverside (92507)	$236k	$199k–$278k
Santa Cruz (95060)	$244k	$207k–$288k

By finish level (Los Angeles, 90026)

Finish	Likely	Range
Basic	$234k	$198k–$276k
Mid	$246k	$209k–$288k
Premium	$270k	$229k–$317k

By option (mid finish, Los Angeles)

Option	Likely	Range
Garage conversion	$172k	$144k–$205k
Attached room addition	$245k	$208k–$289k
New detached ADU	$246k	$209k–$288k

Where the money goes (likely, Los Angeles)

Materials, with sales tax	$65,600
Labor at local billed rates	$85,800
Contractor markup on materials	$9,800
General contractor overhead and profit (Cement mason,Carpenter,Roofer,Glazier,Drywall installer,Electrician,Plumber,HVAC mechanic,Floor layer,Painter,Tile and stone setter trades)	$32,300
Contingency	$23,200
Design, engineering and city fees you pay directly	$20,500

Time on site: about 51 crew days; roughly 14–30 weeks start to finish. City plan check for ADUs and additions commonly takes 2 to 6 months; state law sets a 60-day review clock for complete ADU applications.

How the numbers are built

Local labor
Each trade at the hourly rate contractors bill in your county: BLS wages, payroll taxes, California workers' comp rates for that trade, and contractor overhead and profit.
Real product prices
Materials priced from public store pages, each with its link and the date checked (latest 2026-10-29), plus waste and your county's sales tax.
Honest ranges
Low, likely and high from 4,000 simulated outcomes, not one number that sounds more certain than it is.

Open the free estimator to change the size, finish and ZIP, leave out or add line items, and print a scope sheet for contractor bids. Method and sources.

Questions

How much does an ADU or room addition cost in California?

For a 600 sq ft detached ADU with one bathroom and a full kitchen, our mid-finish likely budget is $232k to $265k across eight California cities (Fresno lowest, San Jose highest). Your own size, finish and ZIP change this; the free estimator recalculates it line by line.

Why do costs vary so much by city?

Mostly labor. We price each trade at the hourly rate a contractor bills in your county, built from Bureau of Labor Statistics wages, payroll taxes, California workers' comp rates and contractor overhead. Sales tax and permit fees also vary by county and city.

Does the estimate include permits and contractor profit?

Yes. Permit fees are estimated from the job's valuation (this project usually needs none). When three or more trades are involved, a general contractor overhead and profit line is shown separately; single-trade jobs are priced at the trade's billed rate only.

Is this a quote?

No. It is a budget estimate, not a bid, appraisal, or insurance claim valuation. Get written bids from licensed contractors, and check licenses with the Contractors State License Board.

Other cost guides

Remodel Estimator is self-serve budgeting software from Caissonix, in pilot. Budget estimate, not a bid, appraisal, or insurance claim valuation. Figures computed 2026-10-29 from price book 2026-10-29.2; they change as prices and wages are updated. Get licensed contractor bids, and check a contractor's license with the Contractors State License Board before you sign.