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ADU Cost Calculator
Estimate your build costs, permit fees, and monthly rental income potential. Works for detached ADUs, attached ADUs, garage conversions, and JADUs across California.
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How ADU Costs Break Down
Building an ADU in California involves four main cost buckets. Understanding each helps you budget accurately and avoid surprises mid-project.
Construction
70–80% of totalLabor and materials: framing, foundation, roofing, MEP (mechanical, electrical, plumbing), drywall, and finishes.
Permits & Fees
$5,000–$25,000Plan check fees, building permits, school impact fees (waived under 750 sq ft), and utility connection fees.
Design & Plans
$5,000–$20,000Architect or designer fees, structural engineering, Title 24 energy compliance reports, and survey if needed.
Site Work
$5,000–$50,000+Grading, drainage, access improvements, utility trenching. Steeply sloped lots or tight access drives costs up significantly.
Common Questions About ADU Costs
How much does it cost to build an ADU in California?
The average ADU in California costs between $150,000 and $450,000, depending on type, size, and finish level. Garage conversions typically run $80,000–$150,000. Detached new construction ranges from $200,000–$500,000+. Permit fees add another $5,000–$25,000 depending on your city.
What is the cost per square foot to build an ADU?
In California, ADU construction costs $225–$550 per square foot. Basic finishes run $225–$300/sqft, standard finishes $300–$400/sqft, and premium finishes $400–$550/sqft. High-cost areas like the Bay Area and Los Angeles tend toward the higher end of these ranges.
Are ADU permit fees included in the cost estimate?
Yes. This calculator adds an estimated $5,000–$20,000 for permit fees on top of construction costs. Your actual permit fees depend on your city — use our Permit Fee Estimator for a city-specific figure.
What factors affect ADU build cost the most?
The biggest cost drivers are: (1) ADU type — garage conversions are far cheaper than new detached construction; (2) Size — every extra square foot adds cost; (3) Finish level — premium kitchens and bathrooms add significantly; (4) Site conditions — slopes, poor soil, or difficult access raise costs; (5) Location — labor costs vary widely across California.
Does a JADU cost less than a full ADU?
Yes. A JADU (Junior ADU) is carved from existing space inside your home, so there is no new foundation or exterior shell. JADU costs typically run $30,000–$100,000, compared to $150,000+ for a new detached ADU.
How much rental income can I expect from an ADU?
California ADU rents vary by location and size. A 400–600 sq ft JADU or studio might rent for $1,200–$2,500/month. A 800–1,200 sq ft detached ADU can command $2,000–$4,500+/month in high-demand markets like Los Angeles, San Francisco, and San Diego.
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