How the home cost calculators work

Questions covered in this guide

Choose the scope before the number

HVAC uses a published national equipment-category range without a square-foot, tonnage, efficiency or ZIP price multiplier. Ductless reference pricing covers cooling only. Heating-and-cooling mini-split scope stays unpriced unless you supply a project range. A supplied range replaces the reference; an extra-work allowance is added once.

Roof area and descriptive choices

The quick roof scenario divides the selected home floor-area range by equally sized above-ground floors, then applies the selected slope range. It does not measure the roof. Garages, overhangs and unequal floors require separate treatment. An unknown answer uses a labeled example assumption. Supplied roof surface measurements override the quick scenario; a horizontal footprint instead uses the factor √(1 + (pitch rise ÷ 12)²).

Units and quantities

Roof totals multiply surface square feet by the selected per-square-foot range and add your allowance. Standard double-hung window estimates use a frame-material table; other window styles use a separate style table. Window totals multiply that single range by the opening count. No frame-by-style multiplier is invented. Supplied unit prices replace the reference.

Unpriced work remains visible

Hidden repairs, permit requirements, electrical work, unusual access, taxes and finishing work can change a real quote. The result lists relevant unknowns. A planning range is not a prediction interval or a promise that a contractor’s price will fall inside it. Save or print the assumptions with the result when comparing written proposals.

Methodology version

Version 2026-10-12.2, prepared October 12, 2026. The reference tables and algorithm are part of the page review fingerprint. Published source notes identify the selected table and access limitations. A source update or a different project scope requires a fresh check.

Compare written contractor quotes

The comparison tool adds each supplied proposal price to confirmed additional charges, with cent rounding, then reports the absolute difference. Blank additional charges are unresolved. Missing or differing scope answers generate questions, and an unchecked comparable-specifications statement keeps the comparison unresolved. There is no market-price adjustment, assumed cost for excluded work or contractor ranking.