Free Tool

ADU Cost Calculator 2026

Calculate your Accessory Dwelling Unit cost by state, size, quality level, and type with ROI and financing estimates.

All 50 statesDetached, attached & garageROI & rental incomeFinancing estimate

Location and Size

200 sq ft1,200 sq ft

1 bedroom ADU

Quality Level

ADU Type

Additional Features

Financing Rate (HELOC / Construction Loan)

5%12%
Estimated ADU Cost
$188,590
California · 600 sq ft · Mid-Range
Low End
$166K
-12%
Estimate
$189K
base
High End
$226K
+20%
Cost Breakdown
Base Construction (600 sq ft × $314/sq ft)$180,090
Permits & Fees (California)$8,500
Total$188,590
Rental ROI (California)
Est. Monthly Rent
$2,200
Net Annual Income
$19,800
Cash-on-Cash ROI
10.5%
Payback Period
9.5 yrs
Financing (20-yr HELOC @ 7.5%)
Est. Monthly Payment$1,519

With $2,200/mo rent, your ADU covers its payment and generates $681/mo net positive cash flow.

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How It Works

How ADU Costs Are Calculated

ADU cost per square foot varies by state due to labor rates, material costs, and permitting requirements. California and Hawaii are the most expensive markets ($150–$300+/sq ft), while southern and midwestern states offer more affordable options ($100–$160/sq ft).

Garage conversions are the most affordable ADU type — you already have a foundation and roof.

Permitting fees vary significantly from $1,000 in rural markets to $9,000+ in Hawaii and California.

Frequently Asked Questions

How much does it cost to build an ADU in 2026?
ADU costs in 2026 range from $80,000 for a basic garage conversion to $350,000+ for a detached high-end unit in California. The national average for a 600 sq ft mid-range ADU is approximately $130,000–$160,000 including permits.
Is building an ADU worth it?
For most homeowners, yes. A properly built ADU in a rental market typically generates $800–$2,500/month in rental income. Payback periods of 7–12 years are common — better than most home improvements.
What is the cheapest type of ADU to build?
Garage conversions are the most affordable ADU option, typically 10–15% cheaper than new construction. You already have a foundation, walls, and roof — the main costs are insulation, drywall, windows, electrical, and plumbing.
How long does it take to build an ADU?
A typical ADU takes 6–12 months from permit application to move-in. Permitting alone can take 2–4 months depending on your city. Garage conversions are faster — often 3–6 months total.
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cost breakdown.

Our full report breaks down all 14 cost categories for your ADU — adjusted to your exact ZIP code and specifications.

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