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California ADU cost calculator

All-in design-build estimates in seconds. 2026 pricing, regionally adjusted. Pick your region, ADU type and size — we'll show the typical range. No email required.

Typical all-in cost
$225,000
$135,000 – $360,000
Per square foot$300 – $500
Region multiplier1.00×
Finish adjustment1.00×
All six ADU types at these settings
ADU typeAll-in cost, low to high
Detached new build750 sqft$135,000–$360,000typical $225,000$180–$480 per sqft
Attached addition750 sqft$112,500–$285,000typical $180,000$150–$380 per sqft
Garage conversion750 sqft$67,500–$180,000typical $112,500$90–$240 per sqft
Junior ADU500 sqft$45,000–$120,000typical $75,000$90–$240 per sqft
Prefab / modular750 sqft$101,250–$270,000typical $168,750$135–$360 per sqft
Basement conversion750 sqft$78,750–$210,000typical $131,250$105–$280 per sqft
Same region, size and finish for every type, except a junior ADU, which state law caps at 500 sqft. Each bar runs from the low to the high estimate, on a scale that starts at $0. The dark mark is the typical cost.
What's included
  • Architecture & engineering
  • Permits & impact fees
  • Construction labor & materials
  • Standard finishes (per finish-level above)
  • Standard utility connections
What can push you 20-40% higher
  • Sloped lots requiring engineered foundations
  • Difficult site access (no driveway for materials)
  • Long utility runs from main house to ADU
  • Tree-protection or hillside review processes
  • Custom architectural features beyond catalog options

This is an estimate. Get at least three real quotes from licensed CA B-class general contractors before signing.

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The estimate on screen when you send this goes with your request (region, ADU type, size, finish level and cost range).

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Based on 2026 published pricing from Maxable, GreatBuildz, Abodu, Angi, BFPM and individual CA design-build firms. Updated quarterly. Cost figures are illustrative — not bids or warranties. See our about page for methodology.

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