Every figure on HomeCostly follows the same process. This page explains it in full so you can judge for yourself how much weight to give our numbers.
For each of our 33 calculators we start with a base low-to-high cost range, set separately for the UK and the USA. These starting ranges are informed by published national trade association data, contractor rate surveys, and material price indices, cross-checked against recent real homeowner spend where it's available.
The base range is then adjusted by the answers you give in the calculator: project size, property type, finish quality, and site accessibility. Each factor is a multiplier grounded in typical trade pricing — for example, difficult site access typically adds 15–25% to labour time, which is reflected in the accessibility multiplier.
Labour and material costs vary significantly by region in both countries. Where you select a region, we apply a regional multiplier calculated from relative cost-of-living and trade wage data for that area versus the national average.
Each project type has a typical materials-to-labour ratio — a boiler replacement, for instance, is mostly labour and margin on the unit itself, while a driveway is closer to an even split. We apply that ratio to the typical cost to produce the breakdown shown in your results.
Calculator figures are reviewed on a rolling basis, at minimum every quarter, and sooner when material costs move sharply (as with timber, copper, or insulation in recent years). See our editorial policy for how that review process works, and our corrections policy for how we handle figures that turn out to be wrong.
An estimate is not a quote. It doesn't know the condition of your specific property, the availability of tradespeople in your area right now, or any complications a surveyor might find. Always get several like-for-like quotes before committing to work — our full disclaimer covers this in detail.