Total cost

What will the whole ADU cost?

Fees are only part of the bill. Add your construction cost per sq ft and any utility work, and we combine them with the official fees for your city. We don’t pick a construction cost for you: enter your own, or use one of the published figures below and adjust it.

City or county

ADU size (interior livable sq ft)

Type Detached Attached Conversion of existing space

Main home size (sq ft) optional

Prorates per-home impact fees above 750 sq ft. Blank = Example assumption of 2,000 sq ft.

Construction cost per sq ft ($)

LowlowHighhigh optional

This figure already includes design and fees

No figure yet? Use a published one ↓ Amounts stay in your browser: never in the URL or analytics.

Utility work not in the city’s fees ($) optional

Things like a new electrical service, trenching or a sewer lateral, from your contractor or utility. City connection charges are already in the fees.

Fee law In force now (2026) From Jan 1, 2027 (SB 1117)

Published construction costs

Use a published figure, then adjust it

We didn’t find an official state figure for ADU construction cost. These are the most authoritative public figures we found. Tap one to fill the cost fields; each is shown with its quoted line. Costs vary a lot with design, site and materials, so treat any of them as a starting point.

San Mateo County ADU Resource CenterA rough all-in figure that already includes design and fees, so we don’t add fees on top when you use it.
Quoted line
a very rough placeholder for you to use is $450-$600 per square foot for construction (“hard costs”) and design and fees (“soft costs”), depending on your design and the materials you chose.
San Mateo County ADU Resource Center (smcadu.org): How much does it cost to build an ADU? (FAQ) (opens in new tab) · checked Oct 18, 2026
UC Berkeley survey of ADU owners: Bay Area medianMedian reported by owners who built ADUs, in a survey published April 2021 and funded by HCD. Not adjusted for inflation since then.
Quoted line
San Francisco Bay Area $177,500 $329.17
UC Berkeley Center for Community Innovation, funded by HCD: Implementing the Backyard Revolution: Perspectives of California’s ADU Owners (Table 2) (opens in new tab) · checked Oct 18, 2026
UC Berkeley survey of ADU owners: Los Angeles County medianMedian reported by owners who built ADUs, in a survey published April 2021 and funded by HCD. Not adjusted for inflation since then.
Quoted line
Los Angeles County $100,000 $197.22
UC Berkeley Center for Community Innovation, funded by HCD: Implementing the Backyard Revolution: Perspectives of California’s ADU Owners (Table 2) (opens in new tab) · checked Oct 18, 2026
UC Berkeley survey of ADU owners: statewide medianMedian reported by owners who built ADUs, in a survey published April 2021 and funded by HCD. Not adjusted for inflation since then.
Quoted line
sample was $150,000, or $250/sf.
UC Berkeley Center for Community Innovation, funded by HCD: Implementing the Backyard Revolution: Perspectives of California’s ADU Owners (Table 2) (opens in new tab) · checked Oct 18, 2026

Example

How the total is built

Example: a 750 sq ft detached ADU at $300–$450 per sq ft is $225,000–$337,500 to build. Add the city’s fees (say $10,000–$15,000) and $15,000 of utility work, and the total is $250,000–$367,500. If a cost figure already includes fees, we don’t add the fees again.

Method →