Two investors walk the same tired duplex on a Saturday morning and come back with rehab numbers $40,000 apart. Neither one is lying. One priced a scope of work line by line and added the money the building burns while it sits empty. The other multiplied square footage by a figure he heard on a podcast.
By the end of this post you will have a repeatable way to estimate rehab costs on a rental property: how to build the scope, how to price it with real local numbers, how much contingency to carry and why, and how to fold in the carrying cost that quietly eats the deal. The method is the same on a $15,000 refresh and a $150,000 gut.
What a Rehab Estimate Actually Is
A rehab estimate is not a number. It is a scope of work with prices attached. That distinction is the whole game. A number can be wrong by half and you will never know why. A scope can be wrong by one line item, and you can see exactly which one.
The scope lists everything that has to happen before a tenant moves in: roof, mechanicals, electrical, plumbing, kitchen, baths, flooring, paint, exterior, permits, trash. Each line gets a quantity and a unit price. Quantities come from measuring. Unit prices come from your contractor, not a national average.
Your offer price, your after repair value, your refinance math, and every return metric in your rental property analysis sit on top of the rehab number. Get it wrong and every other cell in the model is decoration.
The Rehab Budget Formula
Total Rehab Budget = Scope Cost + Contingency + Carrying Cost
Scope cost is the priced line item list. Measure the square footage yourself, count the outlets, look in the panel, get on the roof or pay someone who will. Then take the scope to two or three local contractors and price it as a written document, not a conversation. Three bids on the same written scope are comparable. Three bids on three different verbal descriptions are not.
Contingency is the money set aside for what you cannot see until walls open. It is not padding and it is not optimism insurance. It is a line item with a percentage behind it, and the percentage should reflect how much of the building you actually inspected. Full access, recent inspection, cosmetic scope: ten percent is defensible. Unknown systems, a pre-1978 house, or anything where you could not see behind finishes: fifteen to twenty percent. Foundation work, additions, or a property you bought sight unseen: higher, and you should say out loud why.
Carrying cost is what the property costs you per month while nobody is paying rent. Loan interest, property taxes, insurance at the vacant or builders risk rate, and utilities you now pay because the tenant does not. Multiply the monthly total by a realistic timeline, then add a month. Most investors skip this line entirely, and it is the same line that turns a profitable flip into a break even one. We cover it in depth in how to calculate your true flip profit.
Worked Example: A 1,150 Square Foot Rental
A three bedroom, one bath single family, 1,150 square feet, purchased for $225,000 with a $180,000 interest only rehab loan at 8.5 percent. Scope of work priced from local bids:
- Roof replacement: $11,500
- Furnace and air conditioning: $8,200
- Panel upgrade and partial rewire: $4,400
- Kitchen refresh, cabinets and counters and appliances: $9,800
- Bathroom gut: $7,500
- Flooring, 1,150 sq ft at $6.50 installed: $7,475
- Interior paint: $3,900
- Exterior paint and landscaping: $2,600
- Plumbing repairs: $2,200
- Permits and dumpsters: $1,800
Scope cost: $59,375.
The house is pre-1978 and the seller would not let anyone open a wall, so contingency runs at fifteen percent. $59,375 x 0.15 = $8,906.
Carrying cost over a four month timeline:
- Loan interest: $180,000 x 8.5% ÷ 12 = $1,275 per month
- Property taxes: $3,600 per year ÷ 12 = $300 per month
- Vacant property insurance: $2,400 per year ÷ 12 = $200 per month
- Utilities: $150 per month
Monthly carry: $1,275 + $300 + $200 + $150 = $1,925. Over four months that is $7,700.
Total rehab budget: $59,375 + $8,906 + $7,700 = $75,981.
Notice what happened. The contractor bids totaled $59,375, which is $51.63 per square foot. The number you actually have to fund is $75,981, or $66.07 per square foot. That $16,606 gap is not a cost overrun. It was always there. It just never made it into the spreadsheet.
Why Per Square Foot Rehab Costs Mislead You
Everyone wants a per square foot number because it is fast. The problem is that the number describes an outcome, not an input. Two 1,150 square foot houses can differ by $50,000 because one needs a roof and a panel and the other needs paint and carpet. Square footage does not know that.
It is also the wrong unit for most of the work. A roof is priced by squares, a panel by the job, a furnace by the unit, a bathroom by fixture count. Only flooring and paint scale cleanly with area. Anyone quoting a single all-in dollar per square foot is guessing, and the guess gets worse the more mechanical work the house needs.
Use per square foot as a sanity check after you build the scope, never as the estimate itself. If your line items come to $52 per square foot and your last few rehabs in that neighborhood landed between $45 and $70, the number is plausible. If it comes to $28, you missed something.
The shortcut also ages badly. The producer price index for inputs to new residential construction rose 7.8 percent in the twelve months through August 2026, according to Bureau of Labor Statistics data. A per square foot figure you memorized two years ago is not the same number today.
6 Mistakes That Blow Up Rehab Budgets
1. Estimating from listing photos. Photos hide the roof, the crawlspace, the panel, and the smell. You cannot price what you have not seen, and a seller who will not let you look is telling you something. Fix: walk the property with your contractor before the inspection period ends, or price the unseen systems at full replacement and treat anything better as upside.
2. Leaving carrying cost out of the rehab number. Investors track rehab and debt service in separate places and never add them together for the vacancy period. The money leaves the same account. Fix: build a monthly carry line and multiply by your timeline plus one month.
3. Carrying a contingency you spend in week two. A contingency is for discovery, not for the items you knew about and chose not to price. If you spend it on cabinets you always intended to buy, you are unprotected for the first real surprise. Fix: require yourself to write a one line reason every time you draw on contingency. It stops casual use immediately.
4. Treating every rehab dollar as an immediate deduction. Work that betters, restores, or adapts the property generally has to be capitalized and depreciated, not expensed in year one. That changes your after tax cash flow. The IRS tangible property regulations do include a de minimis safe harbor that lets a taxpayer without an applicable financial statement deduct amounts up to $2,500 per invoice or per item, plus a routine maintenance safe harbor for building work you reasonably expect to perform more than once in the ten year period after the property is placed in service. Fix: code each line as repair or improvement while you build the scope, not in April. Our post on landlord tax deductions most investors miss walks through the distinction.
5. Pricing verbally and calling it a bid. A contractor who says “probably around thirty grand” standing in a driveway has given you a feeling, not a bid. Change orders start where the written scope ends. Fix: issue the same written scope to every bidder and require line item pricing back. Comparable bids are the only kind worth having.
6. Not re-underwriting after the scope changes. The scope always changes. What almost never happens is going back to the model and re-running the deal on the new number. Fix: recompute your cash-on-cash return every time the rehab budget moves more than five percent, and know in advance the number at which you walk. If you are planning to refinance out, the same discipline applies to your BRRRR exit, where a rehab overrun and a soft appraisal compound into trapped capital.
Your Rehab Estimating Checklist
- Measure the property yourself and record actual square footage, room count, and fixture count.
- Write the scope of work as a line item list with quantities before you talk price with anyone.
- Photograph and note the age of the roof, furnace, water heater, panel, and supply lines.
- Send the identical written scope to at least two local contractors and require line item pricing.
- Set a contingency percentage and write the one sentence reason for the percentage you chose.
- Build the monthly carrying cost line and multiply by your timeline plus one month.
- Tag every line as repair or improvement so your tax treatment is decided before the work starts.
- Re-run your return metrics on the total budget, not the contractor bid, and set your walk-away number.
Get the Number Right Before You Sign
Most rehab budgets do not fail because a contractor overcharged. They fail because the estimate was a single number carried in someone’s head, with no scope behind it and no contingency or carry beside it. The fix is structural, and it takes an afternoon.
If you want the math laid out and reusable, our free calculators handle the return side once you have a rehab number you trust. If you are building a repeatable process across multiple deals, our real estate investing coaching covers underwriting discipline, not just the spreadsheet. And if you would rather talk through a specific deal, book a free 20-minute consult.
A good rehab estimate is not the one that comes in lowest. It is the one that still holds when the wall comes down.
Simply Spreadsheets helps real estate investors and small business owners make confident decisions with clean, reliable numbers. Founded by Erin Onsager, a fractional CFO with more than 20 years of finance experience, the firm builds custom spreadsheets, financial models, and analysis that turn raw data into clear answers.
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