How Much Does an ADU Cost in 2026? Real Numbers by Type and State

An ADU is one of the largest discretionary purchases a homeowner ever makes, and the price range is famously wide — anywhere from $60,000 for a simple garage conversion to over $400,000 for a large detached unit in a high-cost market. The number you'll actually pay comes down to three things: the construction type, the size, and where you live.

The single biggest factor: construction type

Per square foot, the type of ADU you build matters more than almost anything else, because it determines how much new structure you're paying for.

• Junior ADU (JADU): $100–$180/sq ft. Carved out of your existing home (up to 500 sq ft), so you reuse the foundation, walls and roof.
• Garage conversion: $120–$220/sq ft. The shell already exists; you add insulation, plumbing, a kitchen and a bathroom.
• Prefab / modular: $180–$300/sq ft including delivery and site work. Factory-built and fast.
• Attached addition: $200–$330/sq ft. Shares a wall with the main house.
• Detached new build: $220–$360/sq ft. Everything is new — the most flexible and the most expensive.

Then multiply by your region

Construction labor and materials cost far more in California, Hawaii, Massachusetts and New York than in Texas, Georgia or Tennessee. A detached ADU that runs $250/sq ft nationally can be $310+/sq ft in coastal California and under $230/sq ft in the South. Our calculator applies a regional cost index for every state so your estimate reflects local pricing.

Don't forget soft costs

Roughly 15–20% of a turnkey ADU budget is 'soft costs': architectural design, structural engineering, permit and plan-check fees, utility connections and impact fees. In California, ADUs under 750 sq ft are exempt from impact fees, which can save several thousand dollars — one reason many homeowners build just under that threshold.

The fastest way to a realistic number is to run your own state, size and type through the free calculator. It returns a low–high range built from 2024–2025 ADU cost data and your state's regional index.