Why Flip Math Is Different From Buy-and-Hold Math
Flipping and long-term rental investing look similar from the outside — both start with buying a property — but the financial engine underneath is completely different. A rental investor cares about monthly cash flow (tracked with tools like the Cash-on-Cash Return Calculator or the Cap Rate Calculator) and long-term appreciation over years. A flipper cares about a much tighter window: how much does this deal cost from purchase to sale, and how much profit is left over once every cost, including the ones that only show up because you're moving fast, gets subtracted?
That's why this calculator is built around a project timeline rather than an annual snapshot. It totals your acquisition cost, your rehab budget, every month of holding costs while the work happens, and your eventual selling costs, then compares the sum against your target after-repair value to show a real profit figure and a real return on the cash you actually put in.
How to Use This Calculator
Flip numbers are only useful if they're grounded in real bids and real comps, not hopeful estimates:
1. Purchase price and ARV
Purchase price should reflect what you'd actually offer, not the list price. ARV (after-repair value) should come from recent, genuinely comparable sales — same neighborhood, similar size, similar finish level — not from the best comp you can find three miles away.
2. Rehab budget
Use contractor bids where you have them. If you're still estimating, add a contingency on top of your best guess rather than using the bare-minimum number — rehab budgets on flips run over more often than they come in under.
3. Financing and hold period
Enter your actual loan terms if you have hard money or a renovation loan lined up. For hold period, be realistic about permitting timelines and typical days-on-market in your area — both tend to run longer than a first-time flipper expects.
4. Check the margin against the 70% rule
Once you have a result, compare your total project cost to 70% of ARV minus rehab — the classic flipper screening rule. If your numbers are well inside that threshold, you likely have room for the unexpected; if you're right at the edge, small surprises can turn a profitable-looking deal into a break-even one.
The Math Behind the Deal
The House Flip Profit Calculator totals every cost in a fix-and-flip deal — acquisition, renovation, financing, and holding — then compares it against your expected sale price to estimate net profit and return on cash invested.
Total project cost
Total Cost = Purchase Price + Purchase Closing Costs + Rehab Budget + Holding Costs + Selling Costs
Holding costs
Holding Cost = (Loan Interest + Taxes + Insurance + Utilities) × Hold Months
Loan interest is calculated as interest-only on your entered loan amount for the hold period — typical for hard money and renovation loans used in flips, which rarely amortize the way a standard mortgage does.
Net profit and ROI
Net Profit = ARV − Selling Costs − Total Project Cost
ROI = Net Profit ÷ Total Cash Invested × 100
Worked examples
Example A — a deal that works despite exceeding the 70% rule. A $220,000 purchase with a $45,000 rehab budget, targeting a $340,000 ARV over a 6-month hold, nets roughly $33,100 in profit after financing and selling costs — about a 39.8% return on cash invested and a 9.7% margin on ARV. Worth noting: the classic 70% rule caps the offer at $340,000 × 70% − $45,000 = $193,000, so this $220,000 purchase price is actually about $27,000 above that threshold. The deal still profits because the ARV margin and financing costs work out favorably — but it illustrates exactly why the 70% rule is a conservative screening heuristic, not a hard requirement. A deal outside it isn't automatically bad; it just carries less cushion for the unexpected.
Example B — the same deal, delayed by three months. Take the identical numbers but stretch the hold period from 6 to 9 months due to permitting delays and a slower resale market. The extra three months of loan interest and carrying costs alone can shave several thousand dollars off net profit — a useful illustration of why hold-period discipline matters as much as the purchase price.
Tips for Best Results
- 💡 Follow the 70% rule as a screening tool Offer no more than 70% of ARV minus repairs to leave room for the unexpected — it's a quick sanity check, not a guarantee.
- 💡 Build in a rehab contingency Add 10–15% to your rehab budget for surprises — older homes especially tend to reveal hidden issues once work begins.
- 💡 Get contractor bids before you buy A rehab budget based on real bids, even preliminary ones, is far more reliable than a per-square-foot rule of thumb.
- 💡 Model a slower sale scenario Run the numbers with an extra month or two of hold time added — if the deal still works, you have real margin for error.
Common Mistakes to Avoid
- ⚠️ Common mistake: underestimating hold time Permitting delays, contractor scheduling, and slow buyer markets can stretch timelines — every extra month adds real holding cost.
- ⚠️ Common mistake: overestimating ARV Base ARV on recent, truly comparable sales — not aspirational comps — since overestimating erases your margin fast.
Frequently Asked Questions
What is the 70% rule in house flipping?
The 70% rule suggests paying no more than 70% of a property's after-repair value minus estimated repair costs, leaving room for holding costs, selling costs, and profit margin.
What costs are included in flip profit calculations?
Purchase price, closing costs on purchase, rehab budget, holding costs like loan interest, insurance, taxes and utilities during the project, and selling costs including agent commissions and closing costs on sale.
What is a good ROI for a house flip?
Many experienced flippers target a 10–20% net profit margin on the after-repair value, though target returns vary based on market conditions, project risk, and financing structure.
How are holding costs calculated on a flip?
Holding costs are typically estimated as a monthly rate covering loan interest, property taxes, insurance, and utilities, multiplied by the expected number of months from purchase to sale.
Does this calculator account for financing costs?
Yes, you can enter a hard money or renovation loan amount and rate, which is factored into your holding costs over the project timeline as interest-only.
What's a realistic profit margin to target on a flip?
Many experienced flippers aim for a net profit of at least 10–15% of ARV before considering a deal worthwhile, since that margin needs to absorb both planned costs and the unplanned ones that come up on almost every project.
How is a flip taxed differently from a long-term rental sale?
Flips held for less than a year are typically taxed at short-term capital gains rates, which are usually higher than the long-term rates that apply to properties held over a year. Because tax treatment depends on individual circumstances, it's worth confirming with a tax professional before finalizing deal math.
Should I include my own labor as a cost in the rehab budget?
Many flippers do, even when doing some work themselves, because it makes the deal's true profitability comparable to a scenario where all labor is contracted out. Skipping this can make a deal look more profitable than it would be if you had to hire out every task.