Why is the range so wide?

Site grading, utility connections, permit fees, and contractor bids change the final number. AduCalc uses ranges — not a single number — so you see the uncertainty up front.

What's the cheapest ADU to build?

A garage conversion on a property with existing utilities is almost always the cheapest path, typically $175–$275 per sq ft. JADUs (500 sq ft carved from your primary home) can also be relatively affordable.

Does California have ADU permit fee caps?

California caps many impact fees for ADUs under 750 sq ft at zero and scales fees for larger units — but local permit, plan-check, and utility fees still apply.

How long does it take to build an ADU in California?

Ministerial review must complete within 60 days under state law. Total project time (design, permit, build) is typically 6–14 months depending on ADU type and city.

CA STATEWIDE · 2026

How much does an ADU cost in California?

Most detached ADUs in California cost $220K–$400K to build. Garage conversions typically run $60K–$150K. Actual numbers depend on your city, finish level, and site work — here's the breakdown.

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STATEWIDE RANGES

California ADU cost by type.

STATEWIDE AVERAGESv2026.04

Scenario	Cost range	Monthly rent	Net payback
Detached · 800 sq ft · mid	$254K–$338K	$1,800–$2,150	12.3–21.2 yrs
Garage conversion · 450 sq ft · mid	$94K–$125K	$1,000–$1,200	8.2–14.2 yrs
Attached · 700 sq ft · mid	$202K–$269K	$1,550–$1,850	11.4–19.7 yrs
JADU · 450 sq ft · mid	$109K–$146K	$1,000–$1,200	9.5–16.6 yrs

MID-RANGE FINISH · YOUR MARKET MAY SHIFT THESE ±5–35%

UPDATED APRIL 2026 · SOURCES

Maintained by the AduCalc editorial team. Cost and rent ranges are directional estimates calibrated from the AduCalc cost engine, 2024–2026 California ADU project data, HCD ADU guidance, RentCafe California rent benchmarks, local MLS comps, and California contractor bid inputs. Final bids vary by site access, utilities, permitting, and finish level.

BY ADU TYPE

Compare the four California ADU types.

DETACHED ADU

$275–$450/sqft

New standalone unit in your backyard. Most privacy, highest rent, highest cost.

TYPICAL · 600–1200 SQFT

GARAGE CONVERSION

$175–$275/sqft

Convert an existing garage. Fastest and cheapest path to permit for most homeowners.

TYPICAL · 300–600 SQFT

ATTACHED ADU

$250–$400/sqft

Added to your primary home. Shares a wall — lower site work cost than detached.

TYPICAL · 500–1000 SQFT

JUNIOR ADU (JADU)

$200–$325/sqft

Up to 500 sq ft carved from your primary home. Owner-occupancy required, permit-light.

TYPICAL · 300–500 SQFT

CALCULATE IT

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01 // LOCATION

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California ADU costs and rents vary a lot by market. Use your city or a ZIP.

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FAQ

California ADU cost FAQs.

A typical 800 sq ft detached ADU in California runs $220K–$360K before site-specific work. Garage conversions run $60K–$150K. Bay Area markets average ~25% higher than Sacramento or the Central Valley.

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