ADU Cost Calculator

Estimate an accessory dwelling unit by type — conversion vs. detached new build.

Quick answer

Total $135,000 — about $67,500 in materials and $67,500 in labor, with a realistic range of $108,000–$162,000 before permit fees.

Calculator

ADU type

ADU size

sq ft

Finish tier

Region cost level

How it works

ADU size × Type-and-tier rate, adjusted by Region = Total

Your ADU size is multiplied by the 2026 per-square-foot rate for its type and tier — $150/$225/$325 for garage conversions, $125/$200/$300 for basement conversions, $250/$350/$500 for detached builds — then adjusted for your region.

Materials ≈ 50% · Labor ≈ 50%

Full construction splits roughly evenly between materials and labor at every tier.

The low–high range follows published rate bands per ADU type. Permit and impact fees ($5,000–$25,000+) sit outside this estimate — confirm them with your city.

Worked example

600 sq ft garage conversion, mid-range finishes:

600 sq ft × $225 = $135,000

Materials (50%) = $67,500

Labor (50%) = $67,500

Range: $108,000 – $162,000

Budget around $135,000 before permit fees.

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Accessory dwelling units went from zoning curiosity to mainstream housing strategy in about five years — and the cost question is the first one everyone asks, because the range is enormous: a garage conversion can run under $150,000 while a detached new build sails past $350,000. Most online 'averages' mash those together into a useless number.

This calculator keeps them separate. Pick the ADU type first — garage conversion, basement conversion, or detached new build — then size and finish tier. Conversions reuse structure you already own; detached builds buy privacy and rental value at new-construction prices.

How to plan an ADU for the cost calculator

Measure the buildable footprint honestly: a two-car garage is typically 400–500 sq ft; that is your realistic ADU size without an addition.
Decide the ADU type first — conversion vs. detached new build changes the cost more than finishes do.
Inventory the expensive unknowns: foundation condition, sewer lateral capacity, and whether the electrical service needs upsizing.
Call your planning department before spending a dollar on design — setbacks, height limits, and owner-occupancy rules vary by city and change fast.

ADU construction cost per square foot (2026 US average)

ADU type	Low	Mid	High
Garage conversion — per sq ft	$120	$150	$180
Garage conversion — mid tier	$180	$225	$270
Basement conversion — per sq ft	$100	$125	$150
Detached new build — per sq ft	$200	$250	$300
Detached new build — mid tier	$280	$350	$420
600 sq ft garage conversion, mid	$108,000	$135,000	$162,000

Complete ADU including kitchen, bath, HVAC, and finishes. Permit/impact fees ($5,000–$25,000) and utility connections are extra and vary by city. Sources: angi.com, houzz.com, thumbtack.com (2026).

Worked example: 600 sq ft garage conversion, mid-range

600 sq ft garage conversion at mid-range finishes, average-cost region:

ADU type: garage conversion; size: 600 sq ft.
Mid-range conversion rate: $225/sq ft.
Total: 600 × $225 = $135,000; region ×1.00 → $135,000.
Materials (50%): $135,000 × 0.50 = $67,500. Labor (50%): $135,000 × 0.50 = $67,500.
Range: 600 × $180 = $108,000 low; 600 × $270 = $162,000 high.

Total $135,000 — about $67,500 in materials and $67,500 in labor, with a realistic range of $108,000–$162,000 before permit fees.

Pro tips for ADU projects

Talk to your city's planning desk first — ADU rules changed in dozens of cities in 2025–2026, usually in your favor.
Get the sewer lateral scoped ($300) — a failed lateral can add $10,000–$20,000 nobody budgeted.
Design for the appraisal: a permitted ADU with its own meter appraises; an unpermitted 'bonus space' does not.
Budget 12–18 months all-in for detached builds — permitting is the long pole, not construction.
If renting it out, check local short-term rental rules before sizing for Airbnb — many cities restrict ADUs to 30+ day stays.

How to use the adu cost calculator

Start with the ADU type: garage conversion is cheapest, detached new build is dearest. Enter the planned size — 400–800 sq ft covers most ADUs. Choose finishes honestly, set your region, and remember the total excludes permit/impact fees, which you should confirm with your city separately.

How adu cost cost is calculated

The estimate multiplies the ADU size by the 2026 per-square-foot rate for its type and tier — $150/$225/$325 for garage conversions, $125/$200/$300 for basement conversions, $250/$350/$500 for detached builds — then applies the region multiplier. Materials and labor split about 50/50; the low–high range follows published rate bands per type.

What drives adu cost cost the most?

ADU type dominates — detached new builds cost roughly double a garage conversion per square foot because you are buying foundation, framing, and roof from scratch. Size matters inversely: small ADUs cost more per square foot (kitchens and baths don't shrink). Finish tier, utility connections (sewer/water/electrical), and your city's fee schedule fill out the rest.

ADU Cost cost example

A 600 sq ft garage conversion at mid-range finishes in an average-cost region estimates at $135,000 — about $67,500 in materials and $67,500 in labor, with a realistic range of $108,000 to $162,000 before permit fees.

Basic vs. mid-range vs. premium ADU finishes

Basic finishes ($150/sq ft for garage conversions) mean rental-grade: stock cabinets, LVP flooring, fiberglass tub-shower. The smart money for a rental ADU — tenants don't pay extra for quartz.

Mid-range ($225/sq ft) is the live-in-it-yourself tier: solid-surface counters, tile shower, decent fixtures. Premium ($325+/sq ft) buys designer kitchens and high-end baths — justifiable for a primary-residence-quality unit or high-end rental markets, but it rarely appraises dollar-for-dollar.

Frequently Asked Questions

How much does it cost to build an ADU in 2026?+

ADUs cost $150–$225 per sq ft for garage conversions, $125–$200 for basement conversions, and $250–$500 per sq ft for detached new builds in 2026. A 600 sq ft garage conversion at mid-range finishes runs about $135,000; a detached unit the same size lands near $210,000.

What is the cheapest type of ADU to build?+

A garage conversion — the existing slab, walls, and roof are already there. Expect $90,000–$195,000 for a complete 400–600 sq ft conversion versus $200,000–$360,000+ for a detached new build of similar size.

How much are ADU permit fees?+

Usually 10–15% on top of construction: plan-check fees, impact fees (many cities now waive these for ADUs under 750 sq ft), utility connections, and surveys. Some jurisdictions total under $5,000; expensive coastal cities can exceed $25,000 — call your planning desk early.

How long does it take to build an ADU?+

12–18 months is typical for a detached ADU: 3–6 months for design and permits, 6–9 months of construction. Garage conversions run 6–10 months all-in. Permitting, not construction, is almost always the long pole.

Does an ADU increase property value?+

A permitted ADU generally appraises and adds value — often $150,000–$300,000+ depending on market — while rental income of $1,200–$2,500/month is common in high-cost metros. Unpermitted space adds far less and can complicate a future sale; permit it.

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