Duplex Construction Cost Calculator

What Drives Duplex Construction Cost

A duplex costs less per square foot to build than two separate single-family houses of the same total size, since it shares one foundation, one roof structure, and often plumbing and electrical runs between the two units — but it still scales with the same two big levers as any new build: total square footage and finish quality. Budget-tier construction (standard finishes, basic fixtures, simpler rooflines) sits well below mid-range, and high-end finishes (custom cabinetry, premium flooring and countertops, upgraded exterior materials) push the per-square-foot number up substantially.

How to Use This Calculator

Enter the combined square footage of both units, pick a finish tier or enter your own rate if you have a local contractor quote to work from, and optionally add a land or site cost if you're budgeting the full project rather than just the build itself.

How We Calculate It

Construction cost = total square footage × your chosen (or entered) rate per square foot. If you enter a land/site cost, it's added on top as a separate line item, since land pricing doesn't scale with the building's finish level the way construction costs do.

A Few Notes

These are rough national ballpark figures for new construction, not a quote — actual costs vary significantly by region (urban markets often run well above these numbers), local labor rates, permitting and impact fees, site conditions like sloped or rocky lots, and how many separate utility connections the project requires. Always get itemized bids from local contractors before committing to a budget, and build in a contingency of at least 10-15% for the kind of surprises that show up once a project actually breaks ground.