How to Underwrite a Flip in 15 Minutes: A Step-by-Step Guide

In fix-and-flip, speed is your competitive advantage. While your competition spends days agonizing over a single potential deal, you need a system to vet properties in minutes. Wasting time on bad deals costs you money and opportunities. The pros don't have a crystal ball; they have a process.

This isn't about cutting corners—it's about ruthless efficiency. It's a repeatable, four-step process for underwriting a flip that separates the tire-kickers from the deal-makers. We'll show you how to find your key numbers, calculate your costs, and make a go/no-go decision while the property is still fresh in your mind. No fluff, no theory, just the high-speed mechanics of profitable deal analysis.

How do you find the After Repair Value (ARV)?

The After Repair Value (ARV) is the estimated market value of the property after all your renovations are complete. It's the single most important number in your entire calculation, as it determines the ceiling for your potential profit.

Finding an accurate ARV is part art, part science. You are trying to predict what a future buyer will pay for the finished product. Your goal is to find recently sold, comparable properties (comps) that are as similar as possible to your target property in its future, renovated state.

What are the best sources for comps?

The best source for comps is the Multiple Listing Service (MLS), typically accessed through a real estate agent. The MLS provides the most accurate, up-to-date sales data, which is what appraisers use. If you don't have MLS access, consumer sites like Zillow and Redfin can provide a quick, preliminary look at recently sold properties in the area, but always verify this data if you decide to move forward on the deal.

Look for 3-5 comps that have sold in the last 90-180 days within a half-mile radius of your subject property. The ideal comp is the same model on the same street, but that's rare. You'll need to make adjustments.

How do you adjust comps for a property?

To adjust comps, you compare a sold property to your target property and assign a dollar value to the differences. You are essentially asking, "What would this comp have sold for if it had the same features as my renovated flip?"

Start with the price per square foot. If a 1,500 sq ft comp sold for $300,000, its value is $200/sq ft. Then, adjust for major features like bedrooms, bathrooms, garages, pools, and overall condition. For example, adding a bathroom might add $10,000-$15,000 to the value, while a superior level of finish (e.g., quartz vs. laminate countertops) could add another $5,000-$10,000. Be conservative with your adjustments.

How do you estimate rehab costs quickly?

Estimating rehab costs quickly requires using reliable cost-per-square-foot averages and knowing which big-ticket items to look for. This number is the biggest variable in your flip, so accuracy is critical. A bad estimate here can wipe out your entire profit.

For a 15-minute analysis, you won't be getting contractor bids. You'll be using tiered estimates based on the level of work required. This is a skill that improves with every property you walk.

What is a good cost per square foot for a flip?

A good starting point for a light, cosmetic rehab is $20-$40 per square foot. For a more standard flip with kitchens, baths, and flooring, budget $40-$70 per square foot. A full gut renovation requiring major system updates can easily exceed $100 per square foot. These figures are highly dependent on your local labor and material costs, which you can research for various markets.

For example, a light cosmetic rehab on a 1,500 sq ft house in a low-cost area might be just $30,000 ($20/sq ft). That same house requiring a new kitchen and two new baths in a market like Tampa, FL could easily be $75,000 ($50/sq ft). Your goal is to categorize the project's scope (cosmetic, standard, gut) and apply the appropriate multiplier.

What are the big-ticket items to watch for?

When you walk a potential property, you must look for the five potential budget killers. These are the major systems where a full replacement can cost $10,000 or more: Foundation, Roof, HVAC, Electrical, and Plumbing. A cracked foundation or an ancient electrical panel can turn a profitable deal into a money pit overnight. If you see signs of trouble with any of these systems—like a sagging roof, old knob-and-tube wiring, or active leaks—you must either get a specialist's opinion or significantly increase your rehab budget to account for the worst-case scenario.

What other costs do you need to budget for?

Many new investors make a critical mistake: they only subtract the rehab cost from the ARV and call the remainder "profit." This is dead wrong. You must account for transactional costs, which can eat up 15-20% of the property's value.

These costs fall into two main categories: holding costs (what you pay while you own it) and closing/sales costs (what you pay to buy and sell it). Ignoring these is a guaranteed way to lose money.

How much are holding costs on a flip?

Holding costs are all the expenses you incur from the day you buy the property until the day you sell it. They typically amount to 3-6% of the purchase price over a 6-month project. This includes loan payments (interest), property taxes, insurance, and basic utilities (water, electricity). The longer you hold the property, the more these costs eat into your profit margin.

How do you calculate closing and sales costs?

Closing and sales costs are the transactional fees required to buy and sell the house, and they can be substantial. These costs typically range from 8-10% of the ARV. When you buy, you'll pay for things like title insurance, escrow fees, and loan origination points (1-2% of purchase price). When you sell, the biggest expense is almost always the real estate agent commissions, which are typically 5-6% of the final sales price. You'll also pay seller-side closing costs, transfer taxes, and potentially staging fees.

How do you put it all together for a final decision?

Once you have your three key numbers—ARV, Rehab Cost, and Other Costs—it's time to make a decision. This is where you move from gathering data to performing deal analysis. A couple of simple tools can make this final step almost instantaneous.

This final check confirms whether the property meets your minimum profit requirements. If the numbers work, you proceed. If they don't, you move on without a second thought.

What is the 70% Rule in flipping?

The 70% Rule is a guideline used to quickly determine the Maximum Allowable Offer (MAO) on a potential flip. The formula is: (ARV x 0.70) - Rehab Costs = MAO. The "30%" buffer is meant to cover your profit, holding costs, and selling costs. While not a substitute for detailed analysis, it's an excellent first-pass filter. If the seller's asking price is significantly higher than your MAO calculated with the 70% rule, the deal is likely not worth pursuing. You can use our 70% Rule Calculator to run this number in seconds.

Example Deal:

* ARV: $500,000

* Estimated Rehab: $60,000

* 70% Rule MAO: ($500,000 x 0.70) - $60,000 = $290,000

If the seller is asking $295,000, it's worth a closer look. If they're asking $350,000, you move on.

How does a deal analyzer speed things up?

A deal analyzer is the key to underwriting in 15 minutes. After you've gathered your ARV, rehab estimate, and cost percentages on the back of a napkin, you plug them into a comprehensive tool like the FlipRuns Deal Analyzer. It instantly calculates your holding and selling costs, itemizes your expenses, and projects your net profit, cash-on-cash return, and ROI.

This removes the guesswork and a mountain of manual calculations. You can see how a 1-month delay in selling impacts your bottom line or how a $10,000 rehab overrun affects your profit. This is how you make an informed, data-backed decision in minutes, not hours.

Example with Analyzer:

Let's take a deal in Austin, TX.

* Purchase Price: $400,000

* ARV: $625,000

* Rehab: $80,000

* Financing: Hard money loan, 20% down

You plug this into the analyzer. It automatically calculates holding costs (approx. $18,000 over 6 months), and selling costs (approx. $50,000 including commissions and fees).

* Total Project Cost: $400k (Purchase) + $80k (Rehab) + $18k (Holding) + $50k (Selling) = $548,000

* Gross Profit: $625,000 (ARV) - $548,000 (Total Cost) = $77,000

Is a $77k profit on an $80k cash investment (20% down) plus rehab costs a good deal? The analyzer tells you instantly, allowing you to make the call and write the offer.

The Bottom Line

Underwriting a flip in 15 minutes isn't about being reckless; it's about having a rock-solid system. It boils down to this: find your ARV, estimate your rehab, account for all other costs, and run the numbers through an analyzer. This process allows you to kill bad deals quickly and focus your energy on the winners. Master this, and you've mastered the most critical skill in real estate investing.

Frequently asked questions

What is the difference between underwriting and deal analysis?

Underwriting is the process of gathering and verifying the key financial data of a potential investment, such as ARV, rehab costs, and market data. Deal analysis is the subsequent step of using that underwritten data to calculate potential profit, return on investment, and risk, ultimately leading to an investment decision.

Can I really trust online estimates for ARV?

No, you should not solely trust automated online estimates (like a Zestimate) for your ARV. These tools can be a starting point, but they often lack accuracy. A reliable ARV is built by analyzing actual, recent sales of comparable properties (comps), preferably from the MLS, and making manual adjustments for differences in size, condition, and features.

How much cash do I need to start flipping houses?

You will need cash for the down payment, closing costs, and a portion of the renovation budget, even when using financing like a hard money loan. A safe range to have on hand for your first flip is typically $50,000 to $100,000+, depending on the price of homes in your market. This covers your initial cash outlay and provides a contingency fund for unexpected expenses.

What's the biggest mistake new flippers make in underwriting?

The biggest mistake is underestimating costs, particularly the rehab budget and holding/selling expenses. New flippers often create an optimistic budget that doesn't account for unexpected repairs or the 8-10% of the ARV that gets consumed by agent commissions, closing costs, and transfer taxes. This single error is the most common reason flips become unprofitable.