How Much Does an ADU Cost?
Get an instant, location-adjusted estimate for your Accessory Dwelling Unit project — including permits, design, and construction.
What's Included
Estimates cover permits, design fees, foundation, framing, MEP systems, and finishes. Site work not included.
Regional Pricing
Costs are adjusted for labor rates and permit fees in your state. California and Hawaii have the highest costs.
Not Included
Utility upgrades, major grading, septic systems, and landscaping can add $5,000–$30,000 to your project.
Get Real Quotes
This calculator gives estimates. Always get 3+ quotes from licensed ADU contractors in your area.
| ADU Type | Low End | High End | Avg per Sq Ft |
|---|---|---|---|
| Detached ADU | $180,000 | $400,000+ | $280–$450 |
| Attached ADU | $140,000 | $300,000 | $220–$380 |
| Garage Conversion | $60,000 | $180,000 | $100–$250 |
| Junior ADU (JADU) | $30,000 | $100,000 | $80–$180 |
| Prefab ADU | $150,000 | $350,000 | $250–$420 |
| Basement Conversion | $80,000 | $200,000 | $150–$280 |
Frequently Asked Questions
Estimates are for budgeting purposes only and may vary by ±15% based on site conditions, contractor, and timing. Always get 3+ quotes from licensed contractors.
How to Use This ADU Cost Calculator
Our free ADU cost calculator gives you an instant, location-adjusted estimate for your accessory dwelling unit project. Simply select your state, choose your ADU type, adjust the square footage, and pick your preferred finish level. The calculator updates in real time, showing you a detailed cost breakdown including base construction, permit fees, design costs, and a contingency buffer.
What Affects ADU Construction Costs?
ADU costs vary enormously depending on your location, the type of ADU you're building, and the complexity of your site. Labor costs in California are 40–60% higher than the national average, which is why the same ADU that costs $200,000 in Texas might cost $350,000 in Los Angeles. Finish level is another major variable — choosing premium finishes over basic ones can add $40,000–$80,000 to a standard detached ADU.
Site conditions that aren't reflected in this calculator — such as steep slopes requiring significant grading, aging utility connections that need upgrading, or mature trees in the construction footprint — can add $10,000–$50,000 to your project. Always have a licensed contractor assess your site before finalizing your budget.
ADU Cost by State
Construction costs vary significantly by state due to differences in labor rates, material costs, and permit fee structures. California, Hawaii, New York, and Washington consistently have the highest ADU construction costs in the country. States like Texas, Arizona, Georgia, and Tennessee tend to have lower construction costs due to lower labor rates and more streamlined permitting.