Know Your Build.
Built by someone who does this for a living, for people about to spend a lot of money.
Know Your Build is made by a project designer at PegArch Architecture and Design, a small Connecticut firm. The site came out of a question clients ask constantly and that nothing online answers well: what is this project actually going to cost me, once the tax bill catches up?
Most online estimators multiply square footage by a number someone averaged years ago in a different state. Connecticut is its own thing. 169 towns, 169 building departments, and a mill rate spread wide enough that the identical addition costs six times as much in one town as another. That is worth getting right.
Mill rates are FY 2025 to 2026 figures for real and personal property, compiled from CT Office of Policy and Management data. 167 of 169 towns are priced. Two had no published current-year rate and are left out rather than guessed at.
Assessment ratio is 70 percent of fair market value, fixed by Connecticut statute.
Construction rates are brackets compiled from published 2026 Connecticut design-build and cost-guide figures, sorted by finish grade. They are starting points, not quotes.
Being straight about the limits is the whole point, so here they are in one place.
- Your assessor sets the real value added, not this site. The estimate applies a scope-based multiplier to construction cost.
- Special fire and taxing district levies are not included. Several CT towns carry them.
- Construction cost varies enormously by room type, site conditions and finish. A bathroom is not a bedroom.
- Motor vehicle rates are capped separately at 32.46 mills and are not shown.
- Nothing here is legal, tax or financial advice. Confirm with your town assessor before you commit money.
An estimate is not a design.
If your project is far enough along that you want real drawings, real numbers and someone accountable for both, PegArch works with homeowners across Connecticut on additions, new builds, ADUs and renovations.
Visit PegArch ↗Know Your Build is not affiliated with, endorsed by, or speaking for any government agency, and mill rate data is reproduced from public CT OPM records without alteration. The site is free to use and carries no advertising. Corrections to any figure are welcome and get fixed quickly.