The 70 percent rule is one of the simplest tools in house flipping, but it only works when you use it with realistic inputs. This guide shows you how to turn the rule into a repeatable calculator for setting your maximum allowable offer, testing rehab assumptions, and adjusting for changing market conditions before you commit to a deal. If you buy distressed property, this is the framework to revisit every time your after repair value, renovation budget, financing costs, or timeline changes.
Overview
A good house flip is usually made or lost before closing. The purchase price sets the ceiling for almost every decision that follows, from your renovation budget to your financing risk to how much room you have if the resale market softens.
That is where the 70 percent rule calculator comes in. In plain terms, the rule helps estimate the most you should pay for a potential flip based on its expected after repair value and its rehab cost.
The basic formula is:
Maximum Allowable Offer (MAO) = ARV x 70% - Repair Costs
Example:
- Expected ARV: $300,000
- 70% of ARV: $210,000
- Estimated repairs: $55,000
- Maximum allowable offer: $155,000
Used properly, this is not a magic number. It is a screening tool. It gives you a fast first-pass answer to an important question: Is this deal even worth deeper analysis?
That matters because flipping houses requires more than finding an ugly property and improving it. As the source material notes, profitable flips depend on buying right, estimating accurately, managing contractors well, securing workable financing, and finding a buyer at the end. The 70 percent rule supports the first two tasks especially well: buying right and analyzing the numbers conservatively.
It also helps solve several common pain points for flippers:
- Overpaying because ARV was too optimistic
- Underestimating rehab costs
- Ignoring holding costs on a flip
- Using a rule of thumb without adjusting for local conditions
The safest evergreen interpretation is this: the 70 percent rule is a useful benchmark, not a universal law. In some neighborhoods, competitive markets, or light cosmetic projects, experienced investors may work from a tighter margin. In slower markets, older housing stock, or higher-risk projects, a stricter threshold may be wiser. Treat the rule as a disciplined starting point rather than permission to skip full deal analysis.
If you want a broader framework beyond the calculator itself, see How to Analyze a Fix and Flip Deal Step by Step and What Makes a Good House to Flip? A Screening Checklist for Buyers.
How to estimate
To build a practical house flipping calculator around the 70 percent rule, break the process into four steps. This keeps you from relying on one headline number while missing the details that protect your profit.
1. Estimate the after repair value
Your after repair value formula starts with comps, not hope. ARV is the price the property could reasonably sell for after the planned renovation is complete.
Use recent, nearby comparable sales that match the finished product you expect to deliver. Focus on homes with similar:
- Size and bedroom/bath count
- Lot characteristics
- Construction style and age
- Level of renovation and finish quality
- School district and micro-location
When doing comps analysis in real estate, it is safer to anchor to the lower end of realistic comparable sales than to the highest sale in the neighborhood. One premium comp can distort your whole project if your finished house will not truly match it.
2. Build a repair estimate
The repair number in the formula should come from a real scope of work, not a rough guess per square foot alone. Even if you use a quick rehab cost estimator in the screening stage, convert that estimate into line items before you make a firm offer.
Your renovation scope should include:
- Demolition and cleanup
- Framing or structural repair if needed
- Roof, windows, siding, and exterior work
- Electrical, plumbing, and HVAC
- Kitchen and bath updates
- Flooring, paint, trim, doors, and fixtures
- Permit costs and inspection-related work
- Landscaping, staging, and punch-list items
A scope of work template and a contractor estimate template are especially useful here because they force you to think in tasks instead of broad categories. If you skip this step, your MAO may look disciplined on paper while hiding a weak renovation budget.
3. Apply the percentage rule with context
Once you have ARV and repair costs, you can run the classic formula:
MAO = ARV x 0.70 - Repairs
But a more useful version for real projects often looks like this:
MAO = (ARV x target percentage) - repairs - contingency - known deal-specific costs
That means you may subtract:
- A contingency reserve for unknowns
- Immediate carrying costs if the timeline is long
- Major seller-side closing items you know you will absorb
This is often the difference between a back-of-napkin number and a decision-quality number.
4. Stress test the deal
Before you rely on your maximum allowable offer, run at least three versions of the same deal:
- Best reasonable case: ARV holds, repairs stay on budget, sale is timely
- Base case: ordinary delays and modest extra costs
- Conservative case: resale price slips or rehab scope grows
If the flip only works in the best case, it usually does not work well enough. A healthy house flipping calculator should reveal fragility, not hide it.
For a first-time investor, this discipline matters even more. Many beginner losses come from paying too much at acquisition and then trying to “renovate their way out” of a bad buy. That rarely ends well. If you are new to this, pair this article with Flipping a House for the First Time: Beginner Mistakes That Kill Profit.
Inputs and assumptions
The calculator is only as good as the assumptions behind it. This section explains the inputs that most often change the answer.
After repair value should reflect the finished product you can actually deliver
ARV is not the value of the house after an ideal renovation with unlimited budget. It is the value after your likely renovation, on your timeline, for that buyer pool.
If your project calls for a practical resale-grade finish, do not comp it against the highest-end custom renovation nearby. Likewise, if the property has layout constraints, awkward site issues, or location drawbacks, your ARV should reflect them even after the rehab is complete.
Repair costs should include the full project, not just visible cosmetic work
Many flippers focus on paint, flooring, kitchens, and baths because those are easy to picture and easy to price. The harder costs are often the ones that upset the budget:
- Water intrusion and hidden rot
- Outdated wiring or plumbing
- Foundation or drainage issues
- Permit costs for renovation
- Trash-out, rework, and change orders
A practical rule is to separate your budget into three buckets:
- Known hard costs based on scope and bids
- Unknown-condition reserve for surprises
- Finish allowance for product choices that may shift slightly
This approach makes your house renovation budget more usable than a single lump sum.
The percentage is not fixed forever
The 70 percent rule became popular because it tries to leave room for resale costs, financing, holding costs, and profit. But markets change. In a faster and more predictable resale market, some investors may sharpen pricing. In a slower or more uncertain market, a lower threshold may be more prudent.
The evergreen takeaway is not “always use 70 percent.” It is “always leave enough room for the full cost of the deal and a margin for error.” If you cannot justify the percentage you are using, fall back to more conservative underwriting.
Holding and financing costs still exist even if the formula hides them
A common mistake is assuming the 30 percent spread automatically covers everything. Sometimes it does not.
You should still think through:
- Loan points and interest
- Hard money loan rates or private financing terms
- Property taxes, insurance, and utilities
- Lawn care, winterization, and security
- Agent commissions and seller closing costs
- Staging, photography, and light touch-up work before listing
This is especially important when using fix and flip loans or working with private money lenders for flippers. The longer the flip timeline, the more these carrying costs matter.
Room-by-room ROI should inform your scope, not inflate your ARV
Readers often search for the best renovations for resale, and that is a useful lens once a deal passes the buy test. Kitchen and bath updates can improve marketability, but they should not be used to force a higher ARV unless the local comps support that value. In other words, kitchen remodel ROI and bathroom remodel ROI help shape your renovation plan; they do not rescue an overpaid acquisition.
For project planning help after the purchase, see How to Find Contractors for House Flips: Vetting, Pricing, and Red Flags and House Flip Checklist: From Offer to Closing Day.
Worked examples
Here are three simple examples that show how the same formula behaves under different conditions.
Example 1: Light cosmetic flip
- ARV: $250,000
- Repair estimate: $25,000
MAO = $250,000 x 70% - $25,000 = $150,000
This looks straightforward, but cosmetic projects can still go wrong if the ARV is based on upgraded comps that your finish level will not match. On lighter rehabs, buyers often get more aggressive because the work feels manageable. That competition can tempt you to creep above your MAO. If you do, know exactly why.
Example 2: Mid-level rehab with uncertain systems
- ARV: $325,000
- Repair estimate: $60,000
MAO = $325,000 x 70% - $60,000 = $167,500
Suppose the home is older and the electrical panel, plumbing supply lines, and roof condition are not fully confirmed. A better decision tool would subtract an additional reserve. If you set aside a contingency for unknowns, your operational MAO may be lower than the classic formula suggests.
That is the safer interpretation for real-world underwriting: the rule gives you a ceiling, not a target.
Example 3: ARV changes by a small amount, and the deal shifts quickly
- Original ARV: $400,000
- Revised ARV after comp review: $380,000
- Repair estimate: $70,000
At $400,000 ARV:
MAO = $400,000 x 70% - $70,000 = $210,000
At $380,000 ARV:
MAO = $380,000 x 70% - $70,000 = $196,000
A $20,000 drop in ARV reduced the MAO by $14,000. That is why small errors in your property value estimator work can materially change the offer you should make. In many borderline deals, the issue is not the formula. It is the comp selection.
A simple calculator layout you can reuse
If you want to build this into a sheet or notebook, use these fields:
- Projected ARV
- Target percentage
- Estimated rehab costs
- Contingency reserve
- Known extra deal costs
- Calculated MAO
- Proposed offer
- Difference between MAO and offer
You can then add a second block for sensitivity testing:
- ARV minus 5%
- Repairs plus 10%
- Additional month of holding costs
If the deal still appears workable under those adjustments, you likely have a more durable opportunity.
When to recalculate
The best use of this calculator is not one-time screening. It is repeated decision control. Recalculate whenever any major input changes, especially before you remove contingencies, approve scope changes, or choose your list price.
Revisit your numbers when:
- New comps come in. A fresh sale nearby can change your ARV assumption materially.
- Contractor bids arrive. Early repair estimates should be replaced with line-item pricing as soon as possible.
- You discover hidden work. Mechanical, structural, drainage, or permit-related issues should trigger an immediate MAO review, even if you are already under contract.
- Financing terms move. Changes in rates, points, or draw timing can alter your carrying costs.
- The timeline slips. Longer projects increase holding costs on a flip and can expose you to different market conditions at resale.
- You change the scope. Upgrading finishes, changing layouts, or adding square footage may improve resale appeal, but they also change cost, time, and risk.
- The resale market softens. If buyer demand weakens, your exit assumptions should get more conservative.
A practical operating habit is to run the calculator at four checkpoints:
- Lead stage: quick screening before a showing or serious underwriting
- Offer stage: final MAO before submitting terms
- Pre-close stage: after inspections, bids, and updated comps
- Pre-list stage: to test your likely resale margin against actual costs
This final step is often overlooked. By the time the rehab is finished, you should know whether the original margin survived reality. That helps you improve future offers and build a more accurate flip house profit calculator for your own market.
For many investors, that feedback loop is the real value of the 70 percent rule. It is not just a buying formula. It is a discipline for comparing assumptions against results over time.
Before your next offer, do this:
- Pull three to five realistic finished comps
- Write a room-by-room and systems-based scope
- Separate known costs from contingency
- Calculate MAO using a percentage you can justify
- Stress test the deal with lower ARV and higher rehab inputs
- Walk away if the deal only works on optimistic assumptions
That is how to use a 70 percent rule calculator as a practical buying tool rather than a slogan. In house flipping, discipline at the offer stage is often the cleanest form of risk management.
If you want to compare this buying framework against bigger market questions, read Is House Flipping Worth It in 2026? Profit Margins, Risks, and Market Realities.