Methodology & Data Sources | Home Cost Guide

The single-source-of-truth model

Home Cost Guide runs on one parameterized cost model. The prose answer at the top of each page, the interactive calculator, the by-state table, the itemized breakdown, and the structured data all read from that same model. Because there is only one source, the number in the headline can never drift from the number in the calculator.

For each service, an estimate is the sum of itemized line items — for example a septic system adds up a tank, a drain field, a soil evaluation, excavation, a distribution box, a permit, and a perc test. Each line item carries a low, typical, and high value seeded from published contractor pricing.

How we adjust for your state

Geography changes what a crew costs, not what nationally priced hardware costs. So we move the labor, not the materials. Each line item declares a labor share, and the effective regional factor is:

effective factor = 1 + labor_share × (state_multiplier − 1)

A septic tank, a well pump, or a garage door is priced the same in Mississippi and Hawaii — it is the labor to install it that differs. The state labor multiplier comes from the U.S. Bureau of Labor Statistics (BLS) Occupational Employment and Wage Statistics construction-worker mean-wage ratio by state. Permit fees use a separate, damped state proxy because permits vary more by municipality than by state.

When we do not have data for a location, we fall back to the national average (a multiplier of 1.00) rather than inventing a number.

Where the parameters come from

Our cost ranges are seeded from published cost guides and real, reported quotes, including:

National cost aggregators: HomeAdvisor, HomeGuide, Fixr, Today’s Homeowner, and Angi.
Service specialists such as welldrillingcosts.com and garage-door installers.
Real “I paid $X” data points from homeowner forums and vendor pages.
State labor multipliers from BLS OES wage data; a state build-cost index (247PRO) informs the permit proxy.

The parameterization — how bedrooms pick a tank, how geology scales the per-foot drilling rate, how a state multiplier splits across labor and materials — is our own work.

Validation against real prices

We spot-check each service against three to five published surveys and real quotes. The table below is generated live by the model right now, at the national baseline, next to the published source range it was checked against:

Scenario (national)	Model typical	Model range	Published benchmark
Conventional septic, 3-bedroom	$8,200	$3,850 – $16,500	HomeAdvisor $8,019 avg ($3,589–$12,463); Today’s Homeowner $8,000
Water well, 150 ft, soil	$9,450	$5,300 – $15,650	welldrillingcosts.com $8,950–$14,950; HomeGuide $9,000–$15,000
French drain, exterior 100 ft	$2,500	$1,000 – $3,500	HomeGuide exterior 100 ft $2,800–$6,500
Sump pump, existing pit	$900	$450 – $1,700	Real replacement quotes $461–$1,500
Steel garage door, single	$1,200	$550 – $2,200	Fixr / HomeGuide steel $550–$1,200–$3,200
Torsion spring, single door	$200	$150 – $300	Angi / HomeGuide $150–$250–$350

Every typical sits within roughly 30% of its published benchmark, and most within 10%.

Honest limits

These are representative published ranges, not an exhaustive market survey.
The per-state permit multiplier is a coarse proxy; local permit fees vary by municipality.
Some tank sizes and high-end configurations are interpolated between published price points, and are labeled as estimates.
Estimates are for budgeting. Always confirm with a licensed local contractor.

Refresh cadence

We review the cost-range parameters at least twice a year, and whenever a major aggregator publishes a new annual guide. State labor multipliers are refreshed annually when BLS releases new wage data. If a real quote you send us diverges sharply from a page, we re-check that service right away. This page and every cost guide show a “last updated” date.

The guides

Methodology last reviewed 2026-08-15.