Your County ADU Calculator is a great place to start when developing a budget. It provides a rough estimate of costs and income and will help you understand how choices can impact your budget over time. In general, it is helpful to avoid having a fixed budget total in your head as you explore your options. The cost to build an ADU typically ranges from $30,000 for a simple interior conversion JADU, to $400,000+ for a large detached ADU with high-end finishes on a hillside lot. Cost per square foot is a good way to estimate, though this too can vary — a very rough placeholder for you to use is $300 range per square foot for construction (“hard costs”) and design and fees (“soft costs”), depending on your design and the materials you chose.

See more details about costs – including design, permitting, and construction – in your County Guidebook.