Formula
Base construction cost = project size x project-type cost. Adjusted construction cost = base x location x finish x complexity. Total = construction + soft costs + contingency.
Site policy
Methodology
The calculator is built for early planning, not bid replacement. It uses editable assumptions and transparent multipliers.
Sources
We use public construction cost context, regional cost-index framing, California ADU policy context, Census housing context, and owner-editable local assumptions. State choices are planning averages; city, county, utility, soil, slope, climate, and contractor availability can move the number.
Limits
The calculator cannot inspect site access, soils, existing framing, utilities, city comments, contractor availability, or owner finish selections.
Updates
Cost assumptions live in JSON so the owner can revise base costs, multipliers, soft cost ranges, and city notes without rewriting the site.
Source context
References used for framing.
NAHB 2024 Cost of Constructing a Home survey Used for national construction cost share context and cost category framing. RSMeans City Cost Index Used for regional construction cost-index framing and state-level planning adjustments. California HCD ADU Handbook Used for California ADU permitting context and state-law caveats. U.S. Census Characteristics of New Housing Used for national housing context and methodology guardrails.
FAQ
Plain answers.
Is this a contractor bid?
No. It is a planning estimate that helps you understand the likely budget range before drawings, engineering, city review, and contractor pricing.
Why is the range wide?
Early construction budgets should be ranges because site conditions, structural scope, utility work, finishes, permits, and contractor availability can move the number fast.
Do I need to enter contact information?
No. The estimate appears first. Contact information is only for saving the estimate or asking for a local review.
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