About ToolSite
Free, accurate, and transparent calculators — built by ToolSite Team.
Built for Home Addition Projects
The Home Addition Cost Calculator uses construction cost data from the National Association of Home Builders and HomeAdvisor to give homeowners, contractors, and real estate investors a reliable starting budget — before they talk to a single contractor.
Our Mission
Home addition projects routinely exceed budgets because homeowners start with no baseline. We built this tool to change that — giving anyone a realistic cost estimate in under 60 seconds, free, with no sign-up required.
Sources & Methodology
Every cost figure traces back to published data: the NAHB Construction Cost Survey, HomeAdvisor's True Cost database, and the Angi Home Improvement Cost Database. Regional multipliers reflect real labor rate variation across US markets. We update figures annually.
How We Research and Maintain Cost Data
Construction costs shift with material prices, labor rates, and regional demand. We review all base cost figures and regional multipliers on an annual basis, cross-referencing the NAHB Cost Study, HomeAdvisor project data, and Angi's regional cost database. Any significant change (greater than 10% in any category) triggers an immediate update. All changes are timestamped on the calculator page.
Our blog articles are written by our research team and reviewed for factual accuracy against published industry sources before publication. We do not publish content that contradicts current NAHB or HomeAdvisor data. When sources conflict, we use the more conservative estimate and disclose the range.
Get in Touch
Found an error in a cost figure? Have a regional data suggestion? We review all feedback seriously — accurate data is the whole point.
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