ADU ROI Calculator Guide

A new detached ADU in Ventura County runs $200,000 to $420,000 all in, depending on size and finish level. That figure includes design ($12K to $28K), permits and impact fees ($6K to $14K), site work ($12K to $45K), and construction ($170K to $340K). A garage conversion runs 40 to 55 percent less because the foundation and envelope are already in place.

A new detached ADU in Ventura County runs $200,000 to $420,000 all in, depending on size and finish level. That figure includes design ($12K to $28K), permits and impact fees ($6K to $14K), site work ($12K to $45K), and construction ($170K to $340K). A garage conversion runs 40 to 55 percent less because the foundation and envelope are already in place.

A 700 to 900 sq ft ADU in Camarillo, Ventura, or Thousand Oaks currently rents for $2,100 to $2,850 per month fully furnished or $1,850 to $2,450 per month unfurnished. A 1,100 to 1,200 sq ft two bedroom ADU clears $2,800 to $3,400 per month. Oxnard trends 15 percent lower. Malibu trends 40 percent higher. Short term rentals (under 30 days) remain prohibited statewide through 2027.

For an owner who finances 75 percent of the ADU and rents it long term, the cash on cash yield averages 7 to 11 percent annually after expenses. That compares favorably to any other residential real estate investment available to owner occupiers. For owners who build an ADU with cash, the net yield on investment runs 6 to 9 percent.

California Proposition 13 protects your underlying property tax basis but the improvement itself is reassessed. A $300,000 ADU addition typically adds $3,000 to $3,600 per year in property tax on top of your existing bill. This is the single largest line item that surprises homeowners. We include it in every ROI analysis we prepare.

A financed ADU in Ventura County hits break even (point at which rental income equals all debt service plus expenses) between month 14 and month 22 depending on interest rate and rent level. A cash ADU hits operational break even immediately but full principal recovery takes 9 to 13 years. After break even, the ADU is pure cash flow plus continued appreciation.

Three ways to realize the investment. Hold and rent indefinitely (highest lifetime yield). Move into the ADU and rent the primary home (useful for downsizing retirees). Sell the property at a premium (ADU equipped homes in Ventura County sell 12 to 18 percent above comparable non ADU homes). Most owners who build an ADU hold it for at least five years before evaluating alternatives.