You don't need to be a contractor to estimate a rehab within 15%. You need a repeatable system, and you need to stop guessing on the four systems that blow budgets: roof, HVAC, electrical, and foundation.
Method 1: The per-square-foot tier (use this on the phone)
| Tier | What it means | Cost / sq ft |
|---|---|---|
| Light cosmetic | Paint, carpet, fixtures, clean-out | $15–$25 |
| Standard | Above + kitchen, baths, flooring, some drywall | $25–$40 |
| Heavy | Above + roof, HVAC, electrical or plumbing | $40–$60 |
| Full gut | Down to studs, systems, layout changes | $60–$100+ |
A 1,400 sq ft house needing a standard rehab: 1,400 × $32 = $44,800. This gets you to an offer in 30 seconds on a seller call. Use it to screen, never to sign.
Method 2: The line-item walk (use this before contract)
Big-ticket items, national mid-range ranges for 2026:
- Roof (architectural shingle): $5.50–$9.00/sq ft of roof area — typically $9,000–$18,000
- HVAC full system: $7,000–$12,000
- Electrical rewire + panel: $8,000–$16,000
- Repipe (PEX): $6,000–$12,000
- Water heater: $1,400–$2,600
- Windows: $500–$900 each installed
- Kitchen (mid-grade, full): $12,000–$25,000
- Bathroom (full): $7,000–$14,000
- LVP flooring: $5–$9/sq ft installed
- Interior paint: $2.50–$4.00/sq ft of floor area
- Foundation (pier/settlement): $8,000–$35,000
- Sewer line replacement: $5,000–$15,000
- Mold remediation: $2,500–$8,000
- Full clean-out / hoarder: $2,000–$7,000
The five-minute walkthrough checklist
Photograph and note every one of these. In this order:
- Roof — age, layers, sagging ridge, daylight in the attic
- Foundation — stair-step cracks in brick, doors that don't latch, sloping floors
- Water — stains on ceilings, musty smell, active leaks under sinks
- HVAC — manufacture date on the label, not the thermostat
- Electrical panel — Federal Pacific, Zinsco, or fuses = full replacement
- Plumbing — galvanized or polybutylene = repipe
- Kitchen and baths — count them, price them as units
- Windows — count them
- Exterior — siding, soffit, fascia, grading toward the house
- Junk — estimate dumpster loads at ~$600 each
The contingency rule
Add 15% to whatever you calculate on a standard rehab, 25% on anything vacant, fire-damaged, or older than 1960. This is not padding — it's the statistical reality of opening walls.
Estimate $40,000 on a 1955 vacant house? Present $50,000 to your buyer. When your buyer's contractor comes in near your number, you become the wholesaler they answer the phone for.
Estimating on-market and remotely
- Zoom into listing photos on the ceilings and floors, not the staged furniture
- Any listing saying "as-is", "cash only", "investor special", or "needs TLC" is a $30/sq ft floor
- Ask the seller directly: "When was the roof last done? How old is the HVAC? Any plumbing or electrical work in the last ten years?" Sellers answer honestly far more often than beginners expect
- Google Street View history shows roof and exterior condition over time
What to never do
Never take the seller's repair number. Never take an unverified "my cousin will do it for $15k" number. And never let a buyer renegotiate you on repairs without photos — if your estimate was documented and honest, hold your fee.