Fix and Flip Guide: How the Numbers Work and Where Flips Go Wrong

Introduction

Flipping is the most visible strategy in real estate investing and the least forgiving. Rental mistakes are absorbed slowly, over years of cash flow. Flip mistakes are realized at closing, in one number, and there is no hold-and-wait option once the carrying costs start compounding.

TL;DR: A flip is a short-duration, high-fixed-cost project where margin is set at purchase and destroyed by time. Budget renovation from contractor bids rather than per-square-foot rules, count every holding and transaction cost, and treat the timeline as the primary risk.

Where the money actually goes

The headline arithmetic — buy at 200, spend 50, sell at 320 — leaves out the costs that consume most of the apparent spread.

Cost	Typical magnitude	Frequently omitted?
Purchase price	—	No
Purchase closing costs	1–2% of price	Sometimes
Renovation	Project-specific	Underestimated
Renovation contingency	10–20% of budget	Yes
Hard money interest	10–14% annualized	Partly
Hard money points	2–4% of loan	Yes
Property taxes, insurance, utilities	Monthly, throughout	Yes
Selling agent commission	2.5–6%	Sometimes
Seller closing costs / concessions	1–3%	Yes

The items marked in bold are where beginner projections break. A flip that looks like a $70,000 spread routinely nets closer to $25,000–$35,000 once financing costs, holding costs and selling costs are counted honestly — and that is on a project that goes to plan.

The 70% rule, and what it hides

The standard screen:

Maximum offer = (After-Repair Value × 0.70) − Renovation cost

On a property with a $400,000 ARV and $60,000 of work, that gives a maximum purchase price of $220,000. The 30% haircut is intended to absorb financing, holding, and selling costs and still leave profit.

It is a screening tool, not an underwriting method, and it fails in predictable ways:

• In high-value markets the 30% haircut is far more than the fixed costs require, and the rule screens out workable deals.
• In low-value markets it is not enough, because transaction and holding costs do not scale down proportionally with price.
• On long timelines it breaks entirely — holding cost is a function of months, and the rule has no time variable.
• It assumes ARV is known. ARV is an estimate, and it is the input that most often turns out to be wrong.

Use it to decide what to look at. Underwrite the deal properly before you offer.

Estimating ARV

ARV is the most important number in a flip and the easiest to inflate.

Use closed sales, not active listings — a listing is an asking price and may be aspirational. Use comparables sold within the last three to six months, in the same submarket, of similar size, age, bedroom count and condition. Match the finish level you actually intend to deliver, not the best comp in the neighbourhood.

Two disciplines protect you:

Respect the ceiling. Every neighbourhood has a price above which buyers stop appearing regardless of finish quality. Renovating past the ceiling spends money that cannot be recovered.

Check absorption. How long did those comps take to sell? A market where comparable homes sit for 90 days has a materially different holding cost than one where they sell in 14, and your exit assumption needs to reflect it.

Building a renovation budget that survives contact

Per-square-foot rules are for screening. Real budgets come from a scope of work and contractor bids.

Order the work by risk rather than by visibility:

1. Structural and systems — foundation, roof, electrical, plumbing, HVAC. Highest cost variance and highest chance of discovery once walls open.
2. Envelope — windows, siding, exterior doors.
3. Kitchens and baths — where buyer perception concentrates.
4. Cosmetic — flooring, paint, fixtures, landscaping.

Then add a contingency of 10–20%, higher on older properties. This is not padding. Older houses reliably reveal work that was not visible at inspection: knob-and-tube wiring behind plaster, a subfloor rotted under a leaking shower pan, cast iron drain lines at the end of their life.

Get three bids on anything material. Verify licensing and insurance, and never fund significantly ahead of completed work — a draw schedule tied to inspected milestones is the single best protection against a contractor walking mid-project.

Permits matter more here than anywhere else. Unpermitted renovation work discovered at resale can stop a sale outright, and it will surface — buyers' agents and appraisers look for it. The cost of doing work under permit is far below the cost of remediating it later.

Financing

Hard money is the default for flips: fast, asset-based, and structured for short holds, at 10–14% annualized plus 2–4 points. Expensive by design, and appropriate because the hold is measured in months. The points are a fixed cost regardless of how quickly you exit, which is why very short flips carry a higher effective annualized cost than the headline rate implies.

Private money — individual lenders — is often cheaper and more flexible, and depends on relationships you build before you need them.

Conventional financing is generally unsuitable: too slow for competitive purchases, and lenders are reluctant on properties needing significant work.

Cash eliminates financing cost and maximizes speed, at the cost of concentration — one flip instead of two or three.

Whichever route, model the interest on the actual expected timeline plus a delay scenario. Interest accrues on the full drawn balance while the property produces no income.

Time is the main risk

Every month of holding costs interest, taxes, insurance and utilities. On a $250,000 hard money loan at 12% with $600 a month in taxes, insurance and utilities, an extra 60 days costs about $6,200 — a meaningful share of a realistic flip profit.

Timelines slip for a small number of recurring reasons: permit approval delays, contractor availability, long-lead materials, discovery of unforeseen structural work, and the property sitting on market after completion. The first four are manageable with scheduling discipline. The last is a market risk, and it is why absorption belongs in the underwrite.

Sequence work so that trades are not waiting on each other, order long-lead items at the start of the project rather than when they are needed, and pull permits before the closing where the jurisdiction allows it.

Taxes

Flips are generally treated as inventory in a trade or business rather than as investment property. The practical consequences: profit is taxed as ordinary income, not long-term capital gains; self-employment tax may apply; and a 1031 exchange is not available, because property held primarily for resale does not qualify. Investors who assume flip profit will be sheltered by an exchange are usually surprised. Confirm treatment with a CPA before the first project, not after.

What actually goes wrong

1. ARV was optimistic. The most common single cause of a disappointing flip.
2. No contingency. The renovation surprise was normal; the budget's inability to absorb it was not.
3. Over-improving past the neighbourhood ceiling. Money spent that the market will not return.
4. Holding costs left out of the model. Especially on a first project.
5. Contractor risk. Overpaid ahead of work, or unvetted and unlicensed.
6. Unpermitted work. Cheap during renovation, expensive at resale.
7. Buying in a thin market. Few comparable sales means both ARV and timeline are uncertain.

Alternatives worth comparing

Flipping is not the only way to profit from a distressed purchase. Wholetailing — light cosmetic work and a fast resale — carries far less renovation risk and shorter exposure, at a lower margin. BRRRR uses the same acquisition and renovation skills but refinances and holds rather than selling, converting the project into a long-term asset and deferring the tax event.

If your edge is finding and renovating undervalued property, all three use it. They differ in exit, tax treatment and risk duration.

FAQ

How much cash do I need to start?

With hard money at 80–90% of purchase and some renovation funding, expect to bring the remaining purchase equity, points, and a meaningful share of renovation cost — plus reserves for overrun and a longer hold. Financing does not remove the need for liquidity.

What is a realistic profit target?

Rather than a fixed number, target a margin that survives a stress case: 10% over on renovation, 60 extra days of holding, and a 5% lower sale price. A deal that still works under all three is a deal.

How long should a flip take?

Three to six months from purchase to sale is typical for a moderate cosmetic-to-mid renovation. Structural work, permit-heavy scopes and slow markets extend it. Model your expected timeline and a delayed one.

Is flipping passive?

No. It is an active project-management business with concentrated risk and a short feedback loop.

Should my first project be a big one?

No. A smaller, mostly cosmetic project in a liquid market teaches the process — contractors, permits, draws, listing — with far less exposure while you are learning where your estimates are wrong.

Conclusion

Flips are won at purchase and lost on time. The margin is set the day you buy, and every week after that erodes it through interest and carrying cost. Estimate ARV from closed comparables at your actual finish level, budget renovation from bids with real contingency, count every financing, holding and selling cost, and treat schedule slippage as the primary risk rather than an inconvenience.

Do that consistently and flipping is a legitimate business. Skip any of it and it becomes an expensive way to buy yourself a job.

Sources

• IRS guidance on dealer vs. investor classification for real property.
• IRS Publication 544, Sales and Other Dispositions of Assets.

Next step: check the 70% rule against the profit you actually need.