Home Project Estimator

Most people get sticker shock not because contractors are overcharging, but because the number in their head never included labor, demolition, permits, or the inevitable surprise behind the wall. This tool builds those line items in from the start.

The calculation starts with a base cost per square foot that varies by project type and material grade. A mid-range kitchen runs about $135 per square foot nationally; a basic interior paint job runs about $4. Labor is split out as a fraction of that base — painting is labor-heavy at around 70%, while a room addition splits closer to 55/45. That split matters when you are comparing quotes, because a labor-heavy project is more vulnerable to local wage variation.

Demolition and permit costs are added as flat adjustments on top of the base. Permits scale loosely with project size but are capped at typical municipal ranges ($500 to $2,000). Finally, a contingency percentage is applied to the subtotal — not the base cost alone — so it grows with the full scope of work. The result is a center-point estimate with a realistic low and high range of plus or minus 15% to 25%.

Use this estimator when you need a defensible number before you call a contractor. It gives you enough information to know whether a project is in your budget range and to spot quotes that are dramatically out of line with market rates. It is also useful for prioritizing competing projects — if you are choosing between a kitchen remodel and a basement finish, comparing rough cost estimates helps you sequence the work.

This tool is appropriate for scoping residential renovation work in the US. It is not appropriate for new construction, commercial projects, or projects requiring structural engineering, which have fundamentally different cost structures. It is also not a substitute for a detailed contractor scope of work — no estimator can account for your specific site conditions, access constraints, or local subcontractor availability.

Stop trusting this estimate when: the project involves a historic property with preservation requirements, the house has known major issues like foundation movement or significant water intrusion, or the project budget exceeds $150,000. At that scale, the variance in real quotes will be wide enough that a ballpark figure stops being useful for decision-making.

The most common mistake is treating the base project cost as the total budget. A 200 sq ft bathroom at $175 per square foot is $35,000 before demolition, permits, or contingency. Add all three at standard rates and you are closer to $45,000. The gap between base cost and total budget is typically 20% to 35%, and skipping these line items is why so many renovation projects run over.

A second mistake is applying a too-small contingency to an older home. Homes built before 1980 frequently have knob-and-tube wiring, lead paint, asbestos insulation, galvanized plumbing, or undersized load-bearing members. null of these appear in a contractor estimate until demolition reveals them. A 10% contingency on a 1965 kitchen remodel is not a budget — it is a down payment on the surprises.

A third mistake is scoping the square footage incorrectly. For a deck, use the deck surface area. For a roof, use the house footprint, not the roof slope area. For interior painting, use wall surface area (perimeter times ceiling height, minus doors and windows) — not floor area. Plugging floor area into a wall painting estimate will understate the cost by 30% to 50% depending on ceiling height and room layout.

The formula runs in four stages. First, a base project cost is calculated: base cost per sq ft times square footage. Second, optional line items are added: demolition at $4.50 per sq ft and permits between $500 and $2,000 depending on project size. Third, a contingency amount is calculated as a percentage of the subtotal (base cost plus demolition plus permits). Fourth, the total is the subtotal plus the contingency.

The cost range shown is the center-point estimate adjusted down 15% for the low end and up 25% for the high end. This asymmetry is intentional — renovation costs almost always surprise to the upside, not the downside. The low-end scenario assumes everything goes smoothly; the high-end scenario assumes one significant unexpected finding.

Labor and materials are shown as a split of the base project cost only — they do not include demolition or permit costs, which are their own categories. The labor fraction varies by project type based on the skill intensity of the work. Painting is 70% labor. Flooring installation is 40% labor. These ratios help you read contractor quotes: if a bid shows unusually low labor on a painting job, ask why.

The cost-per-square-foot model breaks down at the edges of project size because it treats fixed costs as variable. Every project carries overhead that does not scale — mobilization, setup, permit application time, final inspection, and the contractor's minimum job size. On a 40 sq ft bathroom, those fixed costs might represent 30% of the total. On a 400 sq ft bathroom, they are 5%. The per-square-foot number looks identical in both cases, but the smaller project will almost always run higher than the model predicts. When estimating small-scope work, add a flat $1,500 to $3,000 for fixed overhead before applying any contingency.