ADU Cost Calculator
Use this ADU cost calculator to get a rough range based on published cost guides. Pick an ADU type, enter a size, and choose whether to include site work. The result is an estimate from national sources, not a quote or a local bid. Fees, utilities, and site conditions can move the number a lot.
How the estimate works
The calculator multiplies your size by a published cost per square foot for your ADU type [1]. If you include site work, it adds a published range for site prep, utilities, installation, and finishing [2]. Those numbers are national averages. Newer sources report higher costs than the 2023 guide, with some site-built ADUs at $300 to $500 or more per square foot [2]. So treat the low end of any result with care.
What the estimate leaves out
- City permit, plan check, and inspection fees. See City of San Diego fees on our ADU cost guide.
- Development impact fees and school fees, which vary by project.
- Design or plan license fees, unusual site work, and upgrades.
Get a real number
Only a contractor who sees your lot can give you a real price. Request builder quotes.
We're a referral service, not a contractor, and independent contractors may pay us for referrals.
Sources
- HomeGuide, "How Much Does It Cost to Build an ADU?," November 13, 2023. Fetched 2026-11-11. https://homeguide.com/costs/adu-cost
- Block Renovation, "Prefab ADUs: What is the True Cost Savings," February 4, 2026 (updated June 17, 2026). Fetched 2026-11-11. https://www.blockrenovation.com/guides/prefab-adus-what-is-the-true-cost-savings