ADU Cost & Rent Income Estimator
Ballpark your build cost, monthly rent, and simple payback period before you commit to a design.
A detached ADU typically costs $250-$450/sq ft to build new (a garage conversion is cheaper, $150-$300/sq ft). State law protects units up to 1,200 sq ft, and units of 750 sq ft or less skip most local impact fees. Enter your numbers below for a cost and payback estimate.
Enter your planned square footage, construction type, and the monthly rent similar units get in your area.
ADU Cost & Rent Income Estimator
Estimated Build Cost Range
Annual Rental Income
Simple Payback
How this is calculated
Build cost = square footage × a per-square-foot range ($250-$450 for new detached construction, $150-$300 for a conversion of existing space like a garage), reflecting typical California ranges before permit/utility line items. Annual rental income is your entered monthly rent × 12.
Simple payback divides the midpoint of the build cost range by that annual income — it ignores financing costs, vacancy, maintenance, insurance, and any added property tax from new construction reassessment, so treat it as a rough ballpark, not an investment-grade return calculation.
Units at or under 750 sq ft are exempt from most local impact fees and school developer fees under state law, which can meaningfully lower your all-in cost versus a larger unit — factor that in separately from the range shown here, since exact fee amounts vary by city.
Frequently Asked Questions
How much does it cost to build an ADU in California?
Construction costs typically run $250-$450 per square foot for a detached, new-construction ADU, depending on region, finishes, and site conditions (a garage conversion is usually cheaper, often $150-$300/sq ft). A 600 sq ft unit might cost anywhere from $150,000 to $270,000 all-in.
How big can an ADU be in California?
State law protects a detached ADU up to 1,200 square feet regardless of local zoning, and a local agency cannot cap ADU size below 850 square feet (1,000 sq ft for a unit with more than one bedroom).
How long does it take to pay back an ADU's construction cost from rent?
It depends entirely on your build cost and local market rent, but simple payback (build cost divided by annual rent, ignoring financing costs, vacancy, and taxes) commonly lands somewhere between 8 and 20 years for California ADUs.
Are there fee waivers for smaller ADUs?
Yes. ADUs of 750 square feet or less are exempt from most local impact fees (like transportation and park fees) and school developer fees under state law, which can meaningfully lower total project cost for a smaller unit.
Does this estimator account for permit fees and utility hookups?
Only loosely, through the per-square-foot range you select. Actual permit fees, utility connection/upgrade costs, and impact fees (for units over 750 sq ft) vary significantly by city and should be added separately for a precise budget.
This tool provides an educational estimate only and is not a construction bid or financial advice. Get quotes from licensed local contractors and check your city's current fee schedule before budgeting an ADU project.