Home & Construction category
Material, utility, and project planning calculators for home jobs.
ADU Cost Calculator
Build an early accessory dwelling unit budget from project type and square footage, then add local permit, utility, landscaping, and site-work allowances.
Total ADU cost
$208,000
Construction cost
$180,000
How the math works
A 600 sq ft detached ADU at the model's $300 per sq ft planning rate equals $180,000 of construction. Adding $8,000 of permits, $15,000 of utilities, and $5,000 of site work produces a $208,000 all-in estimate before design, financing, escalation, and contingency.
The built-in rates are scenario assumptions, not local quotes. Check zoning and fee rules with the local jurisdiction, price utility work with the serving agencies, and replace the defaults with written estimates before committing.
EveryCalc calculators are designed for fast, practical estimates with transparent inputs and no required account. We use plain formulas, visible assumptions, and related tools so visitors can check the result from more than one angle.
Results are informational only. For financial, tax, legal, medical, construction, or other high-impact decisions, verify the output against primary sources or a qualified professional.
Learn more about our review process on the EveryCalc methodology page.
Calculation notes and example
ADU cost formula and built-in assumptions
Construction cost equals entered floor area multiplied by the selected planning rate: $130 per square foot for a garage conversion, $200 for an attached ADU, or $300 for a detached ADU. Total ADU cost then adds the permit and impact fees, utility hookups, and landscaping or site-work amounts entered. The rates are scenario defaults rather than market averages and do not automatically include design, financing, escalation, demolition, hazardous-material remediation, or contingency.
Detached ADU budget example
A 600-square-foot detached ADU uses the model's $300-per-square-foot rate, producing $180,000 of construction cost. Adding $8,000 for permits, $15,000 for utility hookups, and $5,000 for landscaping or site work produces a $208,000 total. A 15% contingency on construction would add another $27,000 outside the calculator unless included in one of the entered allowances.
Local feasibility and budget checks
- Confirm zoning, setbacks, height, access, parking, fire, utility, and building-code requirements with the local jurisdiction before final design.
- Price sewer, water, electrical service, trenching, foundation, drainage, and difficult access separately; site work can dominate a small unit's budget.
- Replace the built-in rate with a local concept estimate or bids, and compare all-in cost with realistic rent, vacancy, financing, and appraisal treatment.
Useful companion tools: ADU Rental Income Calculator, ADU ROI Calculator, Rehab Budget Calculator, and HELOC Calculator.
How to interpret the adu cost result
Best use
Use the result to size a project, compare materials, estimate a reserve, or decide whether a contractor quote is in the expected range.
Cross-check
Compare the estimate with local code, site measurements, supplier pricing, utility bills, permit rules, and contractor scopes before buying materials.
Watch for
Project estimates are sensitive to waste, labor, access, climate, soil, and existing conditions. Add contingency when the job cannot be measured cleanly.
This page belongs to the Home & Construction calculator library, so the answer should be read in the context of the decision you are modeling rather than as a universal rule.
Before relying on this adu cost estimate
Most calculator mistakes come from the inputs, not the arithmetic. Use this short audit before you reuse the answer in a spreadsheet, quote, application, or important conversation.
Measure the actual site
Square footage, slope, access, waste, existing conditions, and local material availability can change a project estimate quickly.
Add contingency
Cuts, breakage, delivery issues, weather, permits, and hidden repairs often make the real budget higher than a clean calculation.
Compare with local pricing
Supplier quotes, contractor scopes, code requirements, and permit fees should control the final budget.
Rerun this page after new measurements, contractor quotes, material price changes, permit comments, or scope changes.
Sources used for this calculator
These primary or official references help define the rules, terminology, safety checks, or source documents behind this estimate. Source links were checked in July 2026. They do not turn the calculator output into a quote, appraisal, tax determination, or professional opinion.
- Accessory Dwelling Units case study
HUD USER
Defines common attached, detached, and converted ADU forms; local zoning, building, utility, and permitting rules control feasibility and cost.
How to Use
- Choose garage conversion, attached ADU, or detached ADU to load the calculator's planning cost per square foot.
- Enter the proposed conditioned floor area from your concept plan or local size limit.
- Add project-specific permit and impact fees, utility connection costs, and landscaping or site work.
- Review construction cost separately from the all-in total so you can see which local soft costs drive the budget.
- Replace every default with written local estimates before comparing financing options or contractor proposals.
Frequently Asked Questions
What costs are included in this ADU estimate?
The calculator multiplies floor area by a planning rate for the selected ADU type, then adds the permit and impact fees, utility hookups, and landscaping or site-work amounts you enter. It does not automatically include financing, design, surveys, demolition, hazardous-material work, escalation, or contingency unless you include those costs in an entered allowance.
Why can two ADUs of the same size cost very different amounts?
Existing conditions, foundation and utility distance, access, fire-sprinkler requirements, local labor rates, finish level, energy code, and jurisdiction fees can outweigh the square-foot difference. A conversion may also require structural or utility upgrades that make it less predictable than its starting rate suggests.
Does this calculator determine whether an ADU is allowed?
No. Zoning, setbacks, height, parking, owner-occupancy, utility, fire-access, and building-code requirements are local. Confirm feasibility with the planning and building departments that have jurisdiction over the property before paying for final plans.
How much contingency should an ADU budget carry?
The calculator does not add contingency automatically. Many early budgets test at least a 10% to 20% reserve, with more for conversions, difficult access, uncertain utility work, or incomplete drawings. Use contractor bids and completed design documents to narrow the range.
How should I compare an ADU budget with expected rent?
Use the all-in cost, not construction cost alone. Then model realistic vacancy, operating expenses, financing, and rent in the related ADU income or cash-flow calculators. Rental income and appraisal treatment vary by market and lender.
Related Calculators
ADU Rental Income Calculator
Estimate rent, vacancy, expenses, and income from a planned ADU.
ADU ROI Calculator
Compare the all-in ADU investment with projected annual return.
Rehab Budget Calculator
Build a trade-by-trade renovation budget with contingency and holding costs.
HELOC Calculator
Estimate available home equity and draw-period and repayment payments.
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