How we estimate.
Most cost pages hand you a national average with no explanation of where it came from. This page is the explanation. If you disagree with a number on this site, this is the page that tells you exactly which assumption to argue with.
The short version
Every estimate on WhatsCost is built the same way: a per-trade price band for the option you picked, scaled by the size of your project, adjusted by a regional labor multiplier, then rounded and presented as a range. There is no machine learning and no proprietary black box. It is an explicit model, and the sections below describe each input.
Where the numbers come from
Per-option price bands
Each trade has a low and high installed price for every material or system tier, held in a versioned cost model in this site's source. Bands are seeded from published contractor rate data and trade pricing guides, then narrowed against real quotes as we collect them. They cover materials plus standard installation labor.
Project size
Bands are applied per unit where the trade prices per unit (roof squares, wall square feet, linear feet of gutter, window count) and scaled against a baseline where it does not. Scaling is capped so an unusually large or small entry cannot produce a nonsense number.
Regional labor multiplier
Each city we publish carries one multiplier against a national labor baseline of 1.0. Materials cost roughly the same everywhere; crew rates do not, so this is the only geographic adjustment we make. Every city page states its multiplier in plain language rather than hiding it in the math.
The materials and labor split
Estimates are shown itemized because a single total hides where your money goes. The split shown is a modeled proportion for the trade, not a quote from a specific contractor, and real bids vary around it.
What these estimates deliberately exclude
- Structural repairs discovered after demolition or tear-off, which no estimate can price in advance
- Permit fees, which vary by jurisdiction more than they vary by project
- Asbestos or lead abatement in older homes, which is specialist work priced separately
- Contractor overhead and margin above typical market rates, which is where competing bids genuinely differ
- Emergency or after-hours premiums
- Financing costs, which change the total you pay but not the price of the work
The honest limitation: a model that has never seen your house cannot beat a contractor who has stood in it. These ranges exist so you can tell whether a bid is roughly sane before you sign it, and so you know which questions to ask. They are informational ranges, never quotes, and we will not present them as quotes.
How often this changes
Cost data goes stale. Material prices move with tariffs and fuel, labor moves with local demand, and policy changes can reset a whole trade overnight: the 30% federal residential solar credit expired on 31 December 2025, which moved solar payback from roughly 6–10 years to 9–14 and made every pre-2026 solar cost guide wrong. We review the cost model and the per-city labor multipliers on a rolling basis and re-check trade figures when they move. If you find a number that is out of date, tell us and we will fix it.
Corrections and reuse
If a figure here contradicts what you are seeing in your market, we would rather hear it than not. Journalists, contractors, and researchers are welcome to cite these ranges with attribution and a link. We currently model 12 trades, and the method above is the same for all of them.
Start with a specific trade: roof replacement, window replacement, or bathroom remodel.