CompDesk › New Construction Calculator
Free tool · no sign-up
New Construction Calculator
Planning a spec home or a build on a lot? Enter what the finished house should sell for and what it will cost to build. The calculator works backward to the most you can pay for the lot and still hit your profit target, then shows the profit and cash needed at the seller's asking price.
Have the lot's address? CompDesk values the finished house from new-construction comps, builds the hard costs by phase or from your uploaded plans, and keeps the project timeline.
Your first lookup is free, with no account needed. A free account gets you 3 more.Run a new-build pro forma
1 · The finished house
2 · Build costs
Hard costs: everything to build the house, including site work and the builder's markup if you use one. Soft costs: plans, engineering, permits, impact and tap fees, builder's risk insurance and utilities.
3 · The lot
4 · Construction loan and sale
Interest assumes the lot is financed at closing and construction draws average about 55% outstanding over the build, the same method CompDesk uses.
Estimates for investment analysis. Get builder bids, check zoning and utility availability, and confirm loan terms before you buy a lot.
How a new construction pro forma works
With a flip, you start from the purchase price. With a new build, the lot price is the one number you can still negotiate, so builders work backward: start from what the finished house will sell for, take out every cost of building and selling it plus the profit you need, and whatever is left is the most the lot is worth to you. This is often called the residual land value method.
Financing depends on the lot price too, since a bigger lot means a bigger loan and more interest, so the calculator solves for the lot price exactly instead of subtracting a fixed number.
The five cost buckets
- Land: the lot price and closing costs.
- Hard costs: site work, foundation, framing, roof, systems, finishes and landscaping. Builders often quote this per square foot.
- Soft costs: plans, engineering, surveys, permits, impact and utility tap fees, builder's risk insurance and utilities during construction.
- Financing: construction loan points and interest on the money drawn as the house goes up.
- Selling: agent commissions and seller closing costs.
Worked example
A 2,100 sq ft spec house expected to sell for $525,000, built for $140 per sq ft, with a 7% contingency, soft costs of 10% of hard costs, an 80% construction loan at 10% and 10 months from lot purchase to sale. These are the numbers already in the calculator above.
| Hard costs (2,100 sq ft × $140) | $294,000 |
| Contingency (7%) and soft costs (10%) | $49,980 |
| Selling costs (7% of the sale) | $36,750 |
| Target profit (15% of the sale) | $78,750 |
| Max lot price, after financing and closing costs | $44,335 |
|---|
The seller is asking $50,000. At that price the profit drops to about $72,518, a 13.8% margin, and the project needs about $99,748 of your own cash. So the deal is close: offer near $44,000, find savings in the build, or accept a thinner margin.
Rules of thumb for new builds
- Land share: builders often look for the lot to be somewhere around 15–25% of the finished home's value. It varies a lot by market, and in expensive areas land can be far more.
- Profit target: spec builders commonly aim for a margin in the mid-teens or higher on the sale price, because new construction carries more risk and takes longer than a flip.
- Contingency: 5–10% of hard costs is common; use more for sloped, wooded or rocky lots, or when you're new to building.
- Timeline: count from closing on the lot to closing on the sale. Permitting and selling often add months beyond construction.
Common new-build mistakes
- Pricing the house from resale comps. New construction usually sells for more than older homes nearby. Value it from recent new-build sales.
- Forgetting site costs. Clearing, grading, retaining walls, long driveways, well and septic or utility taps can add tens of thousands on a raw lot.
- Skipping soft costs. Impact fees, tap fees and permits vary widely by county and can be a five-figure surprise.
- Underestimating time. Every month of delay adds interest, insurance and taxes.
- Not checking zoning and utilities first. Confirm the lot is buildable for the house you plan before you make an offer.
Build the full pro forma
CompDesk's New Build tab prices hard costs by phase with installed line items, adds builder O&P and contingency, drafts a budget from your uploaded plans with AI Assistant, tracks project timing, and puts it all in a report for your lender.
New Construction Calculator questions
How do you calculate the max price to pay for a building lot?
Start with the projected sale price of the finished house. Subtract your target profit, hard costs, soft costs, contingency, construction financing, selling costs and lot closing costs. What's left is the most you can pay for the lot and still hit your profit target.
What is a new construction pro forma?
A pro forma is a projection of a project's costs, financing, timeline and profit before you commit. For a new build it covers land, hard costs, soft costs, contingency, the construction loan and selling costs against the expected sale price.
How much does it cost to build a house per square foot?
It depends heavily on the market, the size and the finish level. Get local builder bids for your plans; a per-square-foot number is useful for screening lots but not for a final budget.
What profit margin should a spec home builder target?
Many spec builders aim for a margin in the mid-teens or higher on the sale price, because new construction takes longer and carries more risk than a renovation. Thinner margins leave little room for delays or cost overruns.
What are soft costs in construction?
Soft costs are everything that isn't physical construction: architectural plans, engineering, surveys, permits, impact and utility tap fees, builder's risk insurance, and utilities during the build.