House Flipping Math: The 70% Rule and Deal Underwriting
An expert guide to calculating After Repair Value (ARV), maximum allowable offers, renovation budgets, holding costs, and investor ROI.
The Core Metrics of a Successful House Flip
House flipping—buying a distressed property, renovating it, and selling it at market value—is a lucrative real estate strategy. However, successful flippers do not rely on aesthetic design or instinct to make money. They rely on strict, conservative mathematical underwriting. If you pay too much for a property or underestimate repair costs, your profit margin will be wiped out before you even begin construction.
To analyze a house flip, you must run calculations that determine the maximum purchase price, account for buying and selling transaction fees, forecast monthly carrying costs, and estimate your net return on investment. The foundation of this calculation is the After Repair Value (ARV) and the legendary 70% rule.
The Mathematics of House Flipping: The 70% Rule
The 70% rule is a guideline used by real estate investors to calculate the maximum price they should pay for a distressed property to ensure a safe profit margin.
For example, if a home's estimated ARV is $300,000 and it requires $50,000 in renovations, the 70% rule dictates: MAO = ($300,000 × 0.70) - $50,000 = $160,000. Paying more than $160,000 reduces your buffer and increases the risk of loss.
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| Purchase Price | Rehab Cost | Holding/Closing Costs | Total Project Cost | Projected Net Profit | Return on Investment (ROI) |
|---|---|---|---|---|---|
| $140,000 (Ideal) | $50,000 | $24,000 | $214,000 | $86,000 | 40.2% ROI |
| $160,000 (MAO) | $50,000 | $25,000 | $235,000 | $65,000 | 27.7% ROI |
| $180,000 (High) | $50,000 | $26,000 | $256,000 | $44,000 | 17.2% ROI |
| $200,000 (Risk) | $50,000 | $27,000 | $277,000 | $23,000 | 8.3% ROI |
Understanding Renovation and Holding Costs
Distressed properties require significant capital outlays. Renovation budgets should be categorized into structural repairs (roof, HVAC, foundation, electrical) and cosmetic finishes (kitchens, bathrooms, paint, flooring). Always include a 10% to 15% contingency buffer in your renovation estimate to cover unforeseen issues like mold or water damage discovered behind walls.
Holding costs, or carrying costs, represent the expenses incurred while you own the property. These include property taxes, hazard insurance, utilities (electricity, water, gas), and HOA dues. If you finance the project using a hard money loan, the monthly interest payments are typically the largest component of your holding costs.
Use the House Flipping CalculatorEnter your target property's ARV, expected repair costs, purchase price, project duration, and financing terms to calculate your Maximum Allowable Offer (MAO), detailed holding costs, net profit, and ROI.Frequently Asked Questions
How do I determine the After Repair Value (ARV) of a property?
ARV is calculated by analyzing recent sales (comparables or "comps") of similar homes in the immediate neighborhood (typically within 0.5 miles) that have been renovated. Look for similar square footage, bedroom/bathroom counts, and build style.
Is the 70% rule still valid in hot real estate markets?
In highly competitive markets, investors often adjust the rule to 75% or 80% because inventory is scarce and prices are rising. However, this increases your risk, as a smaller margin leaves less room for errors in renovation budgets or price drops.
What is a hard money loan and why do flippers use them?
Hard money loans are short-term, asset-backed loans provided by private lenders. Flippers use them because they close quickly and fund properties in poor condition that traditional banks refuse to finance. They feature higher interest rates (typically 10% to 14%) and upfront points.
What is the biggest mistake first-time house flippers make?
The most common mistake is underestimating renovation costs and project timelines. First-time investors often assume repairs will be cheaper and faster than they are, or fail to budget for holding costs and buying/selling transaction fees.