ADU Calculator
Run the numbers on your ADU project. Adjust rates, terms, and rental income to see what your investment really looks like — then explore strategies to pay it off faster.
What Does an ADU Cost in Twin Falls?
ADU costs vary widely based on type, size, finishes, and site conditions. Here are the typical ranges for Twin Falls and the Magic Valley area:
Garage Conversion
Converting existing structure. Fastest and most affordable option.
Detached New Build
Custom-built from the ground up. Most design flexibility.
Pre-Fab / Modular
Factory-built and installed on-site. Faster timeline.
* Monthly payments estimated at 10% APR over 25 years, principal + interest. Actual rates depend on your credit, lender, and loan type. Ranges based on national averages of $150-$300/sq ft adjusted for Idaho market conditions.
Get Your Rough Estimate
Fill out the form below with your project details. This gives you a starting point — for a precise budget range, book our Feasibility Check.
Get Your ADU Cost Estimate
What Drives ADU Costs?
Understanding where the money goes helps you make smarter decisions. Here's how a typical ADU budget breaks down:
Hard Costs (85-90% of total)
Direct construction expenses:
- • Labor — approximately 40% of total project cost
- • Materials — lumber, concrete, roofing, siding
- • Mechanical — plumbing, HVAC, electrical
- • Finishes — flooring, cabinets, countertops, fixtures
- • Foundation — concrete work and site prep
- • Utility connections — water, sewer, electric, gas
Soft Costs (10-15% of total)
Planning and preparation expenses:
- • Architectural design — plans and engineering
- • Permit fees — building, electrical, plumbing
- • Impact fees — approximately $6,000-$10,000 in Idaho
- • Inspections — multiple required stages
- • Survey / site assessment — property measurements
- • Contingency — 10-15% recommended buffer
Property-Specific Factors
- • Lot size, shape, and slope
- • Distance from existing utilities
- • Soil conditions and drainage
- • Access for construction equipment
- • Existing structures to work around
- • Setback requirements in your jurisdiction
Design Choices That Affect Cost
- • Square footage (biggest cost driver)
- • Number of bedrooms and bathrooms
- • Kitchen complexity (full vs kitchenette)
- • Finish level (standard vs premium)
- • Accessibility features (ADA compliance)
- • Energy efficiency upgrades
ADU Investment Calculator
Plug in your numbers and see how an ADU pays for itself
Ready to run the numbers?
Enter your home value, ADU cost, and expected rent above to see your investment breakdown.
* P&I at selected rate and term. Property value based on FHFA 20-30% avg for ADU properties. Does not include taxes, insurance, maintenance, or vacancy.
Want a Precise Budget Range?
This estimator gives you a rough starting point. For a detailed, property-specific budget range with good/better/best options, book our ADU Feasibility + Budget Range service. It includes a professional site visit, detailed measurements, and a comprehensive report — and the fee ($250-$750) is credited toward your build.
Get Your Real Numbers
Start with a free Readiness Call, then book a Feasibility Check for a detailed budget range tailored to your property.