How we calculate costs

What the three numbers mean

Every cost page carries a low, an averageand a high. The low and high are the ends of what a homeowner realistically pays for a straightforward version of that job — not the cheapest quote anyone has ever received, and not a worst case with every complication at once. The average sits where it actually falls between them, which is why the marker on the range bar is rarely in the middle.

Why the average is not the midpoint

Most home improvement costs are skewed. There is a floor below which no licensed contractor will work, and a long tail above it made of steep roofs, difficult access and discoveries behind the drywall. So the average usually sits below the midpoint of the range, and the bar shows that honestly rather than centering the figure for tidiness.

Where the numbers come from

This is the part most cost sites leave vague, so here it is plainly. Two different kinds of number are in play, and they do not carry the same weight.

State adjustments are calculated from public wage data.The multiplier for your state comes from the Bureau of Labor Statistics Occupational Employment and Wage Statistics release: mean hourly wages for roofers, painters, plumbers, electricians, carpenters and HVAC mechanics, divided by the national mean. Materials move far less by state than labor does, because materials ship nationally, so they carry a smaller adjustment. Anyone can reproduce this from the same public dataset.

The national ranges are our own estimates. They are compiled from market pricing and from the way each trade actually quotes the job — priced as an installed system where that is how it is sold, per unit where it is not. They have not been audited row by row against a single published price list. Some are built up from wage data rather than estimated, and where that is true the page says so and shows the arithmetic.

We would rather tell you that than present an estimate as a survey. It also means the ranges get better when readers send real invoices, which is the correction we value most.

National, then local

Published ranges are national. Labor varies far more by state than materials do, because materials ship nationally and tradespeople do not. Our calculators apply a state labor multiplier and a state material multiplier to the national rate rather than a single blended adjustment.

The three things a guide works out for you

Below the prose on a cost guide are three calculations. They are all derived from the same two published sources and none of them is a new number we invented; here is exactly what each one does.

1. Pricing it for your job

The estimator takes the guide's own national range — the same low, average and high printed at the top of the page — and multiplies it by your quantity, by a standard-of-work factor, and by your state.

total = national range per unit × quantity × standard × state adjustment

Standard is 0.82 for basic, 1.0 for standard and 1.28 for premium. Those are judgements about the spread between builder-grade and better work, not measurements, and they are applied to the whole figure.

2. Cost by state

The state table uses the wage spread of the one trade that does that job — roofers on a roofing guide, electricians on an electrical one — rather than the six-trade average the calculators use. Roofers and electricians are not paid alike, and not in the same places, so an averaged multiplier would print the same fifty ratios on every page of the site.

wage index = state mean hourly wage ÷ national mean hourly wage
state adjustment = (labor share × wage index) + (1 − labor share)

Only the labor share moves. A state does not have its own price for a bundle of shingles, so a job that is 60% labor in a state paying 20% above the national mean lands about 12% above the national price, not 20%. Where a guide has no measured split we assume 50% labor and the table says so on the page. Where BLS suppresses a state's estimate because the sample is too small, that state is left out rather than filled in with the national figure.

3. The materials trend

The chart is the Producer Price Index series for what the job is made of — asphalt felts for a shingle roof, ready-mix concrete for a slab — over the last five years, read monthly, with the twelve-month change stated beneath it.

It is an index, not a price. It is what producers charge for the material, against a base year, and it is useful for seeing which way the material behind a job has moved. It is not a figure to multiply anything by, and the guide says so beside the chart. The series is linked so you can read it at the source.

What a range cannot tell you

It cannot price your house. Access, pitch, stories, permit rules and how busy your local trade is this month all move a real quote. Use the range to judge whether a quote is in the right territory, then ask the contractor to itemize the parts that put it where it is.