Free ADU Cost Estimator

How Much Does an ADU Cost?

Get an instant, location-adjusted estimate for your Accessory Dwelling Unit. Our calculator uses real construction data and regional pricing to give you a reliable starting point.

Free cost estimates
Updated Q1 2026
Trusted by 50,000+ homeowners

Calculate Your ADU Cost

Adjust the options below to get an instant estimate tailored to your project

Project Details

800 sq ft
200 sq ft1,200 sq ft

Your Estimate

Total Estimated Cost
$598,650
$508,853 – $688,448
±15% range

Cost Breakdown

Base Construction$234,000
Sq Ft Cost (900 sqft)$292,500
Permit Fees$19,500
Foundation$0
Design & Plans$23,400
Contingency (10%)$29,250
Total$598,650
Cost per sq ft: $325

Estimate includes permits, design, and construction for California

Why Use Our ADU Calculator?

Built with real construction data to give you the most accurate ADU cost estimates available.

Region-Adjusted Pricing

Costs adjusted for your state with real labor rates and permit fees, not one-size-fits-all national averages.

Real-Time Calculations

See your estimate update instantly as you adjust project details. No waiting, no page reloads.

Comprehensive Breakdown

See itemized costs for permits, design, foundation, and construction. Covers all 5 ADU types with detailed estimates.

Frequently Asked Questions

How accurate are these cost estimates?
Our estimates are based on real construction data and updated quarterly. They should be within ±15% of actual costs for most projects, but final costs depend on specific site conditions and contractor selection.
Are permit fees included in the estimate?
Yes, our estimates include typical permit fees scaled by your region and ADU type. However, some cities have unique requirements that may add additional costs.
What's not included in these estimates?
Site-specific costs like utility connections, significant grading, or structural upgrades to existing buildings are not included. These can add $5,000–$25,000+ depending on your property.
Which ADU types does the calculator support?
We support all five common ADU types: Detached ADU, Attached ADU, Garage Conversion, Junior ADU (JADU), and Basement Conversion. Each has different base costs, permit fees, and construction requirements.