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 centring 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 labour 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.

What a range cannot tell you

It cannot price your house. Access, pitch, storeys, 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 itemise the parts that put it where it is.