Our data and method
Every estimate is built up from individual costs, not a single price per square foot. Here's how, and where the numbers come from.
Updated October 2026 · How we calculate costs
How an estimate is built
- The house. Framing, windows, siding, systems, insulation, drywall, floors and trim are priced per square foot of finished space at the finish level you choose, with adjustments for style, shape and number of stories. The roof is priced on the footprint.
- Rooms priced as rooms. The kitchen, each bathroom and the laundry are priced as units, because they cost about the same whether the house is large or small.
- Foundation and basement are priced on the footprint, plus finishing for a finished basement and a premium for a walkout.
- Garage, outdoor work and extras are added from your answers.
- Site work depends on the slope of the lot and how it gets water, sewer and power.
- Location. Construction costs are multiplied by a regional factor for labor and materials. Permit, impact and connection fees use typical ranges for the state or area.
- Soft costs. Design (by the path you choose), engineering and surveys, the builder's overhead and profit (15%), and a 6% contingency. If you plan to use a construction loan, interest during construction and closing costs are added.
The range
The likely total is the most probable outcome for the choices you made. The range runs 10% below it and 15% above it, because custom homes overrun their budgets much more often than they come in under. It widens when the lot, utilities or location data are less certain.
Timeline
Design time depends on the design path and complexity. Permit time uses typical review times for the state or area. Construction time scales with finished area and finish level, and adds time for basements, complex shapes, timber framing, cold climates and resort areas.
Your planning report
The written plan on your results page is prepared with the help of an AI model. It works from your answers and your computed estimate, and any idea that changes cost is re-priced with the same calculator before it's shown. It does not set prices itself.
Sources
Unit costs are calibrated against published construction cost surveys, regional cost indexes and current cost guides, then checked against pricing from custom builders in specific markets.
- U.S. Census Bureau, Characteristics of New Housing (2025): contract price per square foot for contractor-built (custom) homes
- NAHB, Cost of Constructing a Home (2024): construction cost shares by stage
- NAHB Eye on Housing: custom-home premium, regional prices, economies of scale, construction times
- U.S. Census Bureau, Survey of Construction: months from permit and start to completion
- U.S. Department of Defense, UFC area cost factors (2026): regional construction cost factors
- California Board of Equalization, Residential Building Costs (2025): quality classes, size and shape adjustments
- Freddie Mac Primary Mortgage Market Survey: mortgage rates
- City and county impact fee schedules: Utah examples include Logan, Nibley, Salt Lake City, Provo, Spanish Fork, Summit County and St. George
- HomeGuide, Angi and Fixr cost guides (2025–2026): line items such as foundations, garages, pools, wells and septic systems
- GeoNames postal codes (CC BY 4.0): city and ZIP code lookup
Limits
An estimate can't see your lot, your plans or the bids in your market on the day you build. Treat it as a planning number and a way to compare bids, not as a price. We update the data at least once a year.