What makes a spec-build pro forma different from a rehab model
A fix-and-flip or BRRRR model is primarily about ARV and rehab budget. A spec-build pro forma is about all of those plus land basis, construction carry (which compounds over a 12–18 month timeline), soft costs that can add 20–30% to your hard cost total, and a sell-through timeline that's entirely market-dependent. Get any one leg wrong and you can turn a 20%+ margin deal into a 5% margin deal — or a loss.
Most first-time spec builders dramatically underestimate soft costs and construction carry. They budget hard costs to the dollar and then absorb $30–60k in permits, engineering, lender fees, and agent commissions they never modeled. Professional developers treat soft costs as a separate category, load every known line item, and then add a contingency on top.
This guide walks through each component in the order you encounter it: land, hard costs, soft costs, carry, sell-through timeline, and then the seven sensitivity cases a lender will run before issuing a term sheet. You can track each phase of your construction budget in real time with TerraLine's construction budget tracker — which flags cost variances before they compound into margin erosion.
Land basis: the number that anchors everything
Land basis isn't just the lot price — it's everything you spend to get the land into a buildable state. For a finished lot in a residential subdivision, that may be close to the purchase price. For a raw parcel, it can include utility installation, road access, lot preparation, and environmental remediation.
In our worked example, the lot is a finished suburban lot purchased for $52,000 with $2,100 in closing costs — a total land basis of $54,100. The test: land basis should represent no more than 15–20% of the finished sale price. At $54,100 on a $650,000 sale price, land is 8.3% — well within range. In high-cost markets, land can be 30–40% of sale price, which requires either a higher margin on hard costs or a different deal structure entirely.
One discipline that separates experienced spec builders: they underwrite the land purchase against a specific finished product and sale price before they close on the lot. They don't buy land hoping to figure out what to build — they model the pro forma first and then bid on lots that fit the numbers.
Hard costs breakdown
Hard costs are the direct construction costs: everything that goes into the physical structure. Below is the line-by-line breakdown for our 2,100 SF conditioned-area, 3/2.5 spec home on a finished lot. All figures are contractor bids, not estimates.
| Cost Line | Amount | Notes |
|---|---|---|
| Site work & excavation | $18,000 | Grading, drainage, utilities rough-in |
| Foundation (slab on grade) | $28,000 | 3,000 SF footprint, 6" slab |
| Framing | $62,000 | $19/SF on 2,100 SF conditioned area + roof system |
| Roofing | $14,500 | Architectural shingle, hip roof, ice & water barrier |
| Windows & exterior doors | $16,000 | Low-E double-pane, fiberglass entry |
| Siding & exterior finish | $18,500 | Hardie board lap + board-and-batten accents |
| HVAC | $19,000 | 2-zone heat pump, ERV, whole-house dehumidifier |
| Plumbing rough & finish | $21,000 | 3 full baths + laundry + exterior hose bibs |
| Electrical rough & finish | $18,500 | 200A service, 40 LED fixtures, panel, EV-ready |
| Insulation | $9,500 | Spray foam rim joists, blown cellulose walls |
| Drywall hang, tape & texture | $14,000 | 2,100 SF × $6.65/SF installed |
| Interior doors & trim | $8,500 | Solid-core doors, craftsman casing & base |
| Flooring | $17,500 | LVP throughout, tile baths |
| Cabinets & countertops | $22,000 | Semi-custom shaker, quartz kitchen & baths |
| Appliances | $8,000 | SS package: range, dishwasher, microwave, refrigerator |
| Painting (int. + ext.) | $9,000 | Two coats interior, full prime + finish exterior |
| Concrete (driveway + walks) | $7,500 | Driveway, front walk, rear patio |
| Landscaping & seeding | $5,500 | Topsoil, sod front, seed rear, shrubs |
| Contingency (10%) | $33,700 | Applied to hard cost subtotal before contingency |
| Hard Cost Total | $370,700 |
At $370,700 in hard costs on 2,100 SF of conditioned area, the all-in hard cost rate is $176.5/SF. For a suburban market with mid-to-upper-mid finishes, that's within the typical $160–$200/SF range for 2024–2026. Luxury markets or high-labor-cost metros can reach $250–$350/SF.
Soft costs breakdown
Soft costs are every dollar spent that doesn't physically go into the building: land acquisition, design, permits, financing, insurance, and transaction costs. First-time spec builders routinely underload this category by $25–50k. Below is the full load for our example deal.
| Cost Line | Amount | Notes |
|---|---|---|
| Land acquisition | $52,000 | Paid at close; recorded basis |
| Closing costs on land | $2,100 | Title, recording, transfer tax |
| Architectural plans & engineering | $9,500 | Full CD set + structural calcs |
| Permit fees | $8,200 | Building, mechanical, electrical, plumbing permits |
| Survey & geotechnical | $3,500 | Boundary survey + soil report |
| Development impact fees | $4,800 | Varies by municipality |
| Lender origination & fees | $8,750 | 2% origination on $350k construction loan + doc fees |
| Appraisal & inspection fees | $2,800 | As-complete appraisal + draw inspections |
| Legal (entity + contracts) | $3,500 | Operating agreement, GC contract review |
| Insurance (builder's risk) | $4,200 | 12-month policy, replacement value |
| Real estate agent commission | $19,500 | 3% seller's side on $650k sell price |
| Closing costs on sale | $5,500 | Title, transfer tax, pro-rated taxes |
| Soft Cost Total | $124,350 |
At $124,350 in soft costs against a $370,700 hard cost base, soft costs represent 33.5% of hard costs. That's on the higher end of a typical range (25–35%) because agent commissions and financing fees are a large absolute number on a $650k sale. This ratio compresses on larger projects but often surprises first-timers working smaller price points.
Construction carry: the cost that most developers undercount
Construction carry is the interest cost on your construction loan — but calculating it accurately is more nuanced than you might expect, because you don't draw the full loan balance on day one. Draws are released in tranches (typically 4–6) as phases complete, so you're paying interest on an average outstanding balance that ramps up over the construction period.
A simplified but accurate approach: assume average outstanding balance equals 55–65% of the total loan over the build period (due to the S-curve draw pattern). Multiply by the annual rate and the time fraction. For our example:
Worked Example — Construction Carry Calculation
Note that the $32,400 in carry is already embedded in the soft cost table above (builder's risk + lender fees). The pure interest component ($25,200) represents about 5.1% of the total hard cost — significant but manageable on a 12-month timeline. Stretch to 18 months and carry approaches $38k; stretch to 24 months and you've added $50k+ to a deal underwritten at 12.
This is why managing your draw schedule tightly matters: delays in draw approval waste carry dollars. TerraLine's construction loan draw schedule tool models the running loan balance and interest cost across your actual draw timeline so you can see the carry impact of delays before they happen.
Sell-through timeline and the full deal summary
In our example, the projected sell-through timeline is:
- Land acquisition → construction start: 45 days (permits in hand pre-acquisition)
- Construction period: 12 months
- List → accepted contract: 45 days (active market assumption)
- Contract → close: 30 days
- Total timeline from acquisition: ~15.5 months
Base Case Deal Summary
A 23.8% gross margin is a solid result for a spec build in 2025–2026. Most active spec builders target 18–25% gross margin; anything below 15% in a base case generally isn't worth the execution risk and capital tie-up relative to alternatives. The sensitivity analysis below tests how much margin erosion you can absorb under realistic stress.
7 sensitivity cases lenders run on every spec-build pro forma
Underwriting officers at regional banks and construction lenders don't just review your base case — they run stress scenarios. If your deal breaks on any single adverse variable, you're unlikely to get a term sheet. Below are the seven cases most commonly applied, with the results for our worked example.
| Scenario | Sale Price | Total Cost | Gross Profit | Margin | What Changed |
|---|---|---|---|---|---|
| Base case | $650,000 | $495,050 | $154,950 | 23.8% | 12-month build, sells at list price in 45 days |
| Rates +200bps | $617,500 | $511,050 | $106,450 | 17.2% | Buyer affordability pressure reduces clearing price by 5%; carry cost rises ~$16k |
| Hard costs +10% | $650,000 | $532,120 | $117,880 | 18.1% | Material/labor spike; margins compress but deal still viable |
| Timeline +3 months | $650,000 | $511,000 | $139,000 | 21.4% | Carry cost adds ~$15,950; 3 extra months at $5,316/mo interest |
| Sale price −5% | $617,500 | $495,050 | $122,450 | 19.8% | Competitive market requires price reduction to move inventory |
| Rent-stall fallback | N/A | $495,050 | (3,550) | −0.7% CoC yr 1 | Lease at $2,400/mo; refi at 75% LTV ($487.5k); $7.5k cash in deal; marginal |
| Full stress combo | $588,000 | $558,000 | $30,000 | 5.1% | Rates +200bps + costs +10% + timeline +3mo + price −9.5%; thin but positive |
What the sensitivity table shows: the deal survives all seven cases with a positive outcome (even the full stress combo at 5.1%), and the rent-stall fallback — while thin — leaves the door open to a hold strategy if the sale market stalls. This is the margin of safety a lender needs to see before committing $350k in construction financing.
The margin of safety framework for spec builders
Every experienced spec builder has a set of non-negotiable thresholds below which they won't pull the trigger. Here are the rules most active developers use:
Base case gross margin ≥ 18%
Below 18% there's insufficient buffer for unexpected costs. If you need a 5% cost overrun to erode your margin from 23% to 18%, you have room to execute. If you start at 15%, you're already in stress territory on day one.
Full stress combo must remain positive
Your deal should survive a scenario where rates rise, costs increase, timeline extends, and sale price falls simultaneously. If the full stress combo produces a loss, the margin of safety is insufficient.
At least one viable fallback exit
Can you rent the property and carry it without negative cash flow? If yes, you have a fallback if the sale market moves against you during the build. If the DSCR on a rental fallback is below 1.0×, you have no exit other than distressed sale.
Cost overrun coverage: 10% hard cost contingency
Budget a 10% contingency on all hard costs before you present the pro forma to your lender. If construction comes in on budget, the contingency becomes additional profit. If it doesn't — and in 90% of builds something surprises you — you're covered.
Carry cushion: model at realistic rate + 100bps buffer
Construction loan rates move. Model carry at the rate your lender quoted plus 100bps as a buffer. If you're paying 12% today and rates spike, the model should still work.
Managing your draw disbursements against the actual budget in real time is how you catch cost variances before they eat into your contingency. See how the draw request process works end-to-end — including what documentation lenders want to see before each disbursement.
What your lender actually wants to see
When you submit a spec-build loan package, the underwriter is checking for four things: (1) a credible ARV supported by comps they can verify, (2) a complete cost budget with signed contractor bids — not estimates, (3) a developer track record or a strong GC with verifiable project completions, and (4) a pro forma that survives stress without producing a loss.
The sensitivity table in this article is exactly what most regional bank underwriters build manually. If you walk in with it already completed — and the numbers hold — you shorten the underwriting cycle significantly. Lenders don't want to be surprised; they want to see that you've already stress-tested your own deal.
TerraLine's platform integrates the pro forma with your live construction budget so lenders can see real-time cost tracking alongside the original underwriting model. When a draw request comes in, the variance from budget is automatically flagged — which is exactly what lenders want from a borrower who's managing multiple projects.
Build your spec pro forma in TerraLine
Model hard costs, soft costs, and carry in one place — then track actual draw disbursements against your budget as the build progresses. Lender-ready reports on demand. Start free — no credit card needed.