New Construction Calculator — Free Build Cost & ROI

A build is land plus hard cost plus soft cost plus the interest you pay while the house is still plywood. The sale price that 'feels right' is often the break-even in costume.

Hard cost is dollars per square foot times size. That number is the most lied-about input in development. Use what your builder billed on the last similar job, not a national average from a podcast. Soft costs sit as a percent of hard — design, permits, utilities, insurance, inspections. Contingency sits on hard plus soft because surprises do not only happen in lumber. Land is a cash line, not a vibe about 'what the lot should be worth later.'

Interest is estimated as basis × rate × months/12. It is a simple carry, not a full construction-loan draw schedule. That is enough at offer time. It is not enough to run a bank's construction budget. If your lender needs an interest reserve, put a rate and a timeline that match the permit reality in your town, not the six-month fantasy.

All-in is land, hard, soft, contingency, and interest. Profit is sale minus all-in. ROI here is profit over all-in — a conservative view that treats the whole stack as capital at work. Break-even sale is all-in. The 20% ROI floor is all-in × 1.2. If your list price is under that floor, you are working for a contractor's wage plus risk. Charge for the risk or do not build.

Square-foot all-in is the number to compare against solds. If finished sales in the neighborhood cannot clear your all-in per foot, you do not have a product problem. You have a basis problem. Smaller house, cheaper spec, cheaper lot, or walk.

Specs creep. A quartz upgrade that 'the buyer will want' is how 20% ROI becomes 8%. Lock the finish level before you lock the lot. Re-run this calculator every time the builder sends an adder.

Land development is the sister tool when you are buying dirt to split. Fix & Flip is the sister when you are renovating instead of building. Do not mix the mental models. New walls have a different risk clock than a kitchen.

The identities

All-in = Land + Hard + Soft + Contingency + Interest
Min sale for 20% = All-in × 1.20

Soft is a percent of hard. Contingency is a percent of hard plus soft.

How people blow the result

• Using a builder's 'from the $180s' as a hard bid.
• Forgetting permit timelines so interest is modeled on 8 months of a 16-month city.
• Treating the 20% floor as greedy. It is how you survive one bad lumber cycle.

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