Free tool · Cost calculator
ADU cost calculator
Estimate your ADU build cost in seconds. Choose your state, build type, size, and finish level — get a 2026 cost range with hard and soft costs broken out. Free, no email required.
Last reviewed: 2026-06-14
1. Which state?
Construction costs vary 25%+ by region.
2. What kind of ADU?
Cost varies dramatically by type.
3. How big?
Over 750 sqft — local impact fees typically apply ($5K–$15K extra).
4. Finish level?
Cabinets, counters, flooring, appliances.
Pick a state and build type to see your estimate.
How the estimate works
We start with a 2026 Los Angeles baseline cost per square foot for each ADU build type — detached, garage conversion, attached, junior ADU, and prefab — sourced from public construction-cost data and permit fee schedules. We then apply two adjustments:
- State cost-of-construction multiplier. California is the priciest market; Washington runs ~5% cheaper, Oregon and Colorado ~15% cheaper, Texas and Arizona ~25% cheaper. These multipliers reflect labor rates, materials logistics, and permitting cost differences.
- Finish level multiplier. Basic finishes (builder-grade materials) cost ~15% less than mid-grade; premium finishes (custom cabinetry, hardwood, high-end appliances) cost ~20% more.
Soft-cost ranges (design, structural engineering, plan check, permits, school fees, utility hookups) are state-specific and based on typical permit-fee schedules. Where applicable, we flag the under-750-sqft fee waiver, which can save $5K–$15K in California under 2026 HCD rules.
The estimate is a planning range — not a quote. Real bids from licensed builders for the same scope routinely vary by 20–40%, and unusual site conditions (sloped lot, alley-only access, distant utilities, mature trees) can add $15K–$50K on top.
Sources
- LA Department of Building and Safety — ADU Standard Plan Program ↗California baseline cost data and permit-fee schedules.
- California HCD — 2026 ADU Handbook ↗Statewide fee-waiver rules (under 750 sqft) effective 2026.
- Apartment List — Los Angeles Rent Report (2026) ↗Used to validate ROI assumptions on the cost guide pages.
- Contractors State License Board (CSLB) ↗License verification for any California ADU builder.
Want deeper cost detail? Read the Los Angeles ADU cost guide or browse our ADU FAQ.
Frequently asked
About the calculator
How accurate is this ADU cost calculator?
It's a good first-pass estimate, not a quote. Estimates use 2026 per-square-foot construction costs from public industry sources, adjusted by state cost-of-construction multipliers and finish level. Real bids from licensed builders typically vary 20–40% between contractors for an identical scope — so use this calculator to size your budget, then get written quotes for the real number.
What does the calculator include?
Both hard construction (foundation, framing, finishes, fixtures, appliances) and soft costs (architectural design, structural engineering, plan check fees, building permits, school facility fees, utility hookups). It does not include the cost of land, the cost of buying out existing tenants, or any unusual site conditions like sloped lots or long utility runs.
Why do costs vary so much between states?
Construction labor is the biggest driver. California — especially LA and the Bay Area — has the highest labor costs in the country, partly because of strong union markets and high cost of living. Arizona and Texas typically run 20–30% lower per square foot for comparable builds. Permit fees, school fees, and impact fees also vary widely by state and city.
Why does staying under 750 sqft save money?
Under California's 2026 HCD rules, ADUs under 750 square feet are exempt from most local impact fees, water/sewer connection charges, and capacity fees. Units under 500 sqft are also exempt from school impact fees. These waivers can save $5,000–$15,000. Most western states have similar fee-reduction tiers for smaller ADUs.
Is this calculator updated for 2026?
Yes — costs reflect 2026 construction-cost data and the 2026 California HCD ADU Handbook (effective January 1, 2026). We review the inputs quarterly and date the page with the last review date at the bottom.
Can I get an exact quote without talking to a builder?
No — no online calculator can. Your real cost depends on your specific lot (slope, access, utility distances), local market conditions at the time you build, your finish choices, and the builders bidding. Use this calculator to set realistic expectations, then submit a quick project description and we'll connect you with up to 3 local ADU builders for actual written quotes. Free, no obligation.