How to Estimate Rehab Costs on a Fix and Flip (Without Guessing)

Of the three numbers that decide a fix and flip — purchase price, after-repair value, and rehab cost — the rehab number is the one the operator controls least and gets wrong most. Purchase price is negotiated. ARV comes from comps. Rehab is a forecast of work that has not happened yet, on a building whose problems are partly hidden behind drywall.

And it is unforgiving. On a deal with a $40,000 projected profit, a 15% overrun on a $90,000 rehab is $13,500 — a third of the margin gone before the first overrun on holding costs or a soft sale. This is why the rehab estimate is not a clerical step. It is the part of the underwrite most likely to be the difference between profit and loss.

This is the line-item method experienced flippers use to turn a guess into a defensible budget.

Step 1 — Set a square-foot baseline by scope tier

Before you price a single line item, classify the scope. The square-foot baseline is not your final number — it is a sanity check that tells you within five minutes whether your detailed estimate is in the right universe.

• Cosmetic ($15–35/sqft): paint, flooring, light fixtures, hardware, landscaping cleanup. Systems are sound. This is a "lipstick" flip.
• Full cosmetic ($35–65/sqft): the above plus a kitchen and bath refresh, some appliances, minor repairs. The most common profitable flip tier.
• Gut ($65–120/sqft): down to the studs in kitchens and baths, new systems (some or all of HVAC / electrical / plumbing), new layout. Real construction.
• Structural / full gut ($120–200+/sqft): foundation, framing, roof structure, full systems replacement, additions. Highest risk tier — see foundation problems.

These ranges vary by market — a gut in coastal California runs double a gut in the rural Midwest. Calibrate to your own labor market using your last two completed projects. The point of the tier is not precision; it is to catch the moment your detailed estimate comes in at $30/sqft for a project you already know is a gut.

Step 2 — Build the line-item budget

Walk the property with a structured list and price each system and room independently. The square-foot number is the top-down check; the line-item budget is the real estimate. Group it the way a contractor would bid it:

• Exterior & structure: roof, siding, windows, foundation, grading/drainage, decks/porches.
• Major systems: HVAC, electrical panel + rewiring, plumbing supply/drain, water heater. See HVAC age math and reading an electrical panel.
• Kitchen: cabinets, countertops, appliances, sink/faucet, backsplash, flooring. Usually the single largest room-level line.
• Bathrooms: per bath — vanity, toilet, tub/shower, tile, fixtures, exhaust.
• Interior finishes: flooring (by area), drywall/repair, interior paint, trim/doors, lighting.
• Specialty: sewer line (get a sewer scope), mold/asbestos abatement, pest, well/septic.

Get one real contractor bid on the largest two line items before you close. A general "I think the kitchen is $20k" from across the room is exactly the kind of estimate that becomes a $34k invoice. The two biggest lines drive the budget; anchor them to a real number.

Step 3 — Add the line items beginners forget

Most rehab estimates that blow up did not blow up on the kitchen. They blew up on the costs that never made it onto the spreadsheet. Add these explicitly:

• Permits and plan fees — can run $2k–15k on a gut, and pulling them late stalls the whole timeline. See permit risks every investor misses.
• Dumpsters and debris removal — $400–700 per pull, and a gut needs several.
• Utilities during the hold — power, water, and gas have to be on for the crew the entire project.
• General-contractor margin — if you are using a GC rather than self-managing trades, add 15–25% on top of the subs' costs.
• Holding costs — loan interest, insurance, and taxes for the full timeline. A delay here is pure margin loss; see the true cost of renovation delays.
• Staging and final cleaning — small numbers that are always forgotten and always spent.

Step 4 — Apply a contingency (this is not optional)

The contingency is not padding. It is the budgeted acknowledgment that you cannot see behind the walls. The right size scales with how much is hidden:

• 10% on a clean cosmetic rehab where systems are confirmed sound.
• 15% on a full cosmetic or any property built 1970–1990.
• 20%+ on a gut, anything pre-1970, or any property where you could not fully inspect the major systems before closing.

The contingency is part of the rehab number you underwrite to — not a separate optimistic buffer you hope not to touch. If the deal only works without the contingency, the deal does not work.

Step 5 — Validate against ARV and the deal math

Now take the all-in rehab number back to the deal. Run it through the 70% rule: max offer = (ARV × 0.70) − rehab. Then check your actual target margin with the full hold modeled, not just the rule of thumb.

If the honest rehab number pushes the deal underwater, that is the answer. The most expensive mistake in flipping is shaving the rehab estimate to make a deal you already want to do come out positive on the spreadsheet. The budget is a verdict, not a target — see why ARV fails for the same failure mode on the value side.

How DealIntel handles the rehab number

DealIntel builds the rehab estimate from the strategy and scope, runs it through the full financial model alongside ARV and financing, and stress-tests the outcome with Monte-Carlo — so a rehab overrun shows up as a P10 / P90 spread rather than a single optimistic point estimate. The 25-point Kill List flags the structural and systems risks (foundation, sewer, panel, roof) that drive the worst overruns, before they become a line item you discover mid-project.

Related reading

• The true cost of renovation delays
• How foundation problems kill profit
• How to analyze a fix and flip deal
• Fix and flip red flags checklist
• ARV calculator