California ADU Cost Calculator

Plan Your Dream ADU Today with Accurate Cost Estimates

Build smarter, not harder! Use our California ADU Construction Cost Calculator to get precise cost estimates tailored to your property and preferences. Whether you’re planning a guest house, home office, or rental unit, we’ll help you calculate costs and make informed decisions.

Factors Affecting ADU Construction Costs

Here’s what impacts the total cost of building an ADU in California:

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ADU Size: 150
Construction Type
Lot Slope
Bedrooms
Bathrooms
Utilities & Finish
Contingency

Please note that this calculator provides an estimate to familiarize you with ADU construction costs. It is not meant to be entirely accurate and should not be interpreted as a final quote.

Why Use Our ADU Calculator?

Get a detailed breakdown of costs based on your ADU size, construction type, and finishes.

Calculate costs specific to your location, lot conditions, and preferences.

Plan ahead with clarity and avoid unexpected expenses.

Ready to Build Your ADU?

Start your journey now! Get an instant cost estimate, tailored to your unique needs, and take the first step toward creating your perfect ADU.

Estimate Your ADU Costs

ADU Size Impacts Costs

The size of your ADU is one of the biggest factors in determining cost. Larger ADUs cost more overall but are more affordable per square foot.

ADU Size (sq ft)Low EstimateHigh Estimate
300 sq ft$37,500$90,000
500 sq ft$62,500$150,000
800 sq ft$100,000$240,000
1000 sq ft$125,000$300,000
1200 sq ft$150,000$360,000

Choose Your Construction Type

The type of ADU project you choose will influence your total cost. Converting existing space is often less expensive than building a new detached unit.

Construction TypeCost Range (per sq ft)
Conversion (garage, attic, basement)$125 - $200+
Attached ADU$150 - $250+
Detached ADU$180 - $300+
Over Existing Structure$200 - $350+

Lot Slope

Building on a sloped lot increases costs due to additional work like grading, retaining walls, and limited access. Expect a 25% higher cost for sloped lots.

Utilities & Interior Finish

The finish level you choose will directly impact costs. Here’s a breakdown:

Finish LevelDescriptionAverage Cost / sq ft
BasicEntry-level fixtures, carpet flooring, vinyl windows.$10 - $20
StandardHigh-quality finishes, granite countertops, stainless steel.$20 - $40
PremiumTop-tier finishes, custom woodwork, and ceramic tiles.$50+

Soft Costs

These planning and administrative expenses are essential for any ADU project:

ServiceAverage Price
Design$2,000 - $30,000+
Architectural Plans$2,000 - $40,000+
Engineering$0 - $5,000+
Permits & Application Fees$1,500 - $8,000+
Impact Fees (over 750 sq ft)$2,000 - $14,000+
Utility Fees$0 - $20,000+
Project Management$0 - $20,000+

Contingency

We recommend setting aside at least 10% of your construction budget for unforeseen costs like material price hikes or supply chain delays.

Testimonials

"Min has provided consulting services to my housing development company. He is excellent in understanding the project and providing the most cost effective solutions. I will definitely use him on my projects."

Zafar M, President P.E, Developer

"Min managed over 30 tenant improvements, build-out of a restaurant, mixed-use apartment building, and all major capital renovation projects starting from contract negotiation to construction management and close-out."

Adam Nathanson President and CEO

"UNI Construction helped my company with getting a permit in the City of LA by providing architectural drawings and helping us with questions that the city was asking. Min was very helpful and very quick to respond, he was able to work on the project with short notice for us, which was incredibly helpful with keeping our client happy. He made sure to continue following up with us regarding the status of the permit."

Yasmine P. Preferred One Plumbing, Los Angeles, CA

"Super good. Quality super top, nice person. Got great deal for permit drawing. Highly recommended."

Sandy U. Consultant, Walnut, CA
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