Spec Home Pro Forma Calculator
Enter the land, the build, the loan, and the sale to see the profit, the equity you need, and how long the home can sit before carry takes the profit.
Land
Hard costs
Soft costs
Contingency and overhead
Financing
Carry per month
Sale
| Layer | Amount | Of sale price |
|---|---|---|
| Land | $123,500.00 | 14.5% |
| Hard costs, contingency, overhead | $452,880.00 | 53.2% |
| Soft costs | $38,000.00 | 4.5% |
| Financing and carry | $44,203.64 | 5.2% |
| Selling costs | $59,640.00 | 7% |
| Profit | $133,776.36 | 15.7% |
How carry eats profit
Each month the home sits unsold costs $4,436.28 in interest on the full loan, taxes, insurance, and utilities.
| Sale \ Hard | -10% | -5% | 0% | +5% | +10% |
|---|---|---|---|---|---|
| -10% | $102,228.62 | $78,384.49 | $54,540.36 | $30,696.23 | $6,852.10 |
| -5% | $141,846.62 | $118,002.49 | $94,158.36 | $70,314.23 | $46,470.10 |
| 0% | $181,464.62 | $157,620.49 | $133,776.36 | $109,932.23 | $86,088.10 |
| +5% | $221,082.62 | $197,238.49 | $173,394.36 | $149,550.23 | $125,706.10 |
| +10% | $260,700.62 | $236,856.49 | $213,012.36 | $189,168.23 | $165,324.10 |
Assumptions and sources
Land and soft costs fund at closing, hard costs draw over the build, and the loan funds its share of each dollar spent. Equity pays points, interest, and carry. Your scenarios stay in this browser, and the page link holds the numbers of the open scenario, not its names.
- Interest rate 9%: the bank prime loan rate of 7.00% plus an example spread of 2 points. Source: Federal Reserve H.15 via FRED (DPRIME), as of Oct 21, 2026.
- Loan to cost 80%, points 1%, taxes, insurance, and utilities of $750 a month. Source: Buildplus example values, not market data. Use the terms from your lender and insurer, as of Oct 27, 2026.
- Land $120,000, hard cost $170 and sale $355 per sq ft, contingency 5%, overhead 6%, commission 5%, seller closing 2%. Source: Buildplus example values for one home. Use your own bids, sales comps, and listing agreement, as of Oct 27, 2026.
Run it before you buy the lot, then again when bids come in. Your scenarios stay in this browser. Updated October 2026. Results are estimates, not financial, legal, lending, or tax advice. See all free contractor tools.
What is a spec home pro forma?
A spec home pro forma is the budget for a house you build before you have a buyer. It adds up land, hard costs, soft costs, financing, and carry, then subtracts them from the expected sale price less selling costs. What is left is the profit. You divide it by the sale price, the total cost, and your equity to see if the deal is worth the risk.
The formula, with the default numbers
| 1 | Sale priceHeated square feet × price per square foot | 2,400 × $355.00 =$852,000.00 |
|---|---|---|
| 2 | Net proceedsSale price − commission and seller closing costs | $852,000.00 − $59,640.00 =$792,360.00 |
| 3 | ProfitNet proceeds − land, hard and soft costs, contingency, overhead, financing, and carry | $792,360.00 − $658,583.64 =$133,776.36 |
What margin to aim for
In the NAHB 2024 Cost of Constructing a Home survey, average builder profit was 11.0% of the sale price. A spec home also carries the risk of a slow sale. Set your target above the margin that two extra months on market and a 5% overrun would take. The carry chart and the sensitivity grid show that number. To price with that margin as a markup, use the markup vs margin calculator.
Hard costs by the square foot
Early in a deal, price hard costs as dollars per heated square foot from homes you have built. When you have bids, switch to line items. Keep design, permits, impact fees, and utility connections in soft costs, so your per square foot number compares to the next home. Use the same lines as the schedule of values on your pay application.
Where spec deals go wrong
Carry
Interest, taxes, insurance, and utilities run every month until the home closes. A build that takes two months longer than planned pays two more months of all of them, on a loan that is close to fully drawn.
Overruns
Hard costs are the largest layer of the stack, so a small miss is a large number. On a $450,000 build, a 10% overrun takes $45,000 of profit before contingency and overhead grow with it. Buildplus cost to complete tracks expenses against the budget as they happen, so you see an overrun while you can still act.
Slow sales
Months on market are the most expensive months, because the loan is fully drawn. Price cuts to move the home come off the top line, and commission still applies to what is left.
Before Buildplus I would have to send my subcontractors multiple payments spread out over a couple of days to avoid hitting electronic transfer limits.
Now I can send one payment and be done. That convenience combined with the fact that payments are automatically tracked back to the right subcontract makes Buildplus a very elegant solution.
Cliff Kahan
Property Projects LLCFAQs
How do I calculate profit on a spec house?
Start with the sale price and subtract commission and seller closing costs. From that, subtract land, hard costs, contingency, overhead, soft costs, loan points, construction interest, and carry. The remainder is profit. Divide it by the sale price for your margin.
What is a good profit margin on a spec home?
NAHB put average builder profit at 11.0% of the sale price in its 2024 survey. A spec home also carries sale risk, so leave room for overruns and a slower sale. Compare the margin with return on equity too, because a thin margin with little cash in can still be a good return.
How much equity do I need to build a spec home?
Equity is the total project cost less the loan. Your lender sets the loan to cost on a spec loan; the 80% default here is an example. You also pay the points, interest, and carry, so plan for more cash than the down payment alone.
How is construction interest estimated in a pro forma?
The loan funds as work is done, so you pay interest only on the drawn balance. This calculator draws land and soft costs at closing and spreads hard costs over the build on an even or S-curve. After the build, interest runs on the full loan until the home sells.
Where are my scenarios saved?
In this browser only. Your numbers are not sent to Buildplus. The page link holds the numbers of the open scenario, not its names, so you can share it. Copy a scenario to compare lots, prices, or loan terms, and download a PDF to send to your lender.
What is Buildplus?
Buildplus is the payments, expenses and invoicing platform built for contractors running cost-plus jobs. Every payment, swipe and reimbursable expense stays tied to the project it belongs to.
© 2026 Buildplus. All rights reserved