How we estimate costs
Every HouseMath calculator is built the same way, so you can compare projects on equal terms.
1. Installed price per unit
For each option on a page, such as a roofing material or a water heater type, we maintain a low and high installed price. Installed means materials and labor together. Prices are per the unit contractors quote in: square feet, linear feet, tons, fixtures or the whole job.
2. Adjustments for your conditions
Some conditions change labor time for the whole job, such as roof pitch, number of stories or site access. The calculator applies these as a percentage adjustment to the base price.
3. Add-ons and fixed costs
Extras you tick, such as removing an old installation or adding a gate, are added on top. Where a job almost always carries fixed costs, such as a permit or disposal, those are included and listed separately.
4. The range and the midpoint
The low end fits a simple job with standard materials in a lower-cost area. The high end fits a complex job, premium brands or a high-cost metro area. The large number on each calculator is the midpoint of your range.
How we check and update figures
We compare our ranges against current installer, manufacturer and retailer pricing and national cost surveys, and we use U.S. Bureau of Labor Statistics wage data to understand how trade labor costs differ by state. All 35 calculators were last reviewed in September 2026. Each page shows the date its figures were last reviewed, and that date changes only when the content changes.
State pages
Our state pages adjust the national range for local labor costs. Labor is typically 40% to 60% of an installed job depending on the trade, so we move only that share by the difference between the state's median wage for the trade (roofers, HVAC installers or carpenters, from the U.S. Bureau of Labor Statistics Occupational Employment and Wage Statistics, May 2025) and the national median. Materials stay at national prices. A state where roofers earn 20% more than the national median therefore shows roof costs about 11% higher, not 20%. This is a planning adjustment, not a survey of local quotes, and prices inside a state still vary by metro area.
Limits of any estimate
No calculator can see your house. Hidden damage, local codes, permit fees and contractor availability all affect real prices. Use HouseMath ranges to plan and to compare quotes, then rely on written quotes from licensed local professionals.
Spotted a price that looks off for your area? Tell us at hello@housemathguide.com.