What Is an ADU Cost Calculator and How Much Does It Cost to Build an ADU in California?

An ADU cost calculator helps California homeowners estimate the cost of building an accessory dwelling unit based on factors like square footage, construction type, utility work, site conditions, and finish quality. In California, ADU construction costs typically range from $100,000 to $200,000, although detached ADUs with premium finishes or difficult site conditions can exceed that range. According to the Terner Center for Housing Innovation, “The median statewide construction cost of an ADU is $150,000, or approximately $250 per square foot,” while “71% of ADUs surveyed cost less than $200,000.” An ADU cost calculator gives homeowners a faster way to estimate realistic project budgets before speaking with designers, contractors, or lenders.