First House Flip: 10 Mistakes Beginners Make and How to Avoid Them

A first house flip usually loses money before the first wall comes down, in the spreadsheet: an ARV (after-repair value) from one comp, no contingency, a rehab guessed per square foot, holding and selling costs forgotten. These ten house flipping mistakes have a fix each, and most fixes are a line in the calculation. The example house below (ARV $320,000, repairs $48,000, bought at $200,000) shows what each mistake costs.

Mistakes in the numbers before you buy

1. Taking the ARV from one comp

ARV (after-repair value) is what the house should sell for once the work is done. One sold house nearby that fetched $340,000 is not an ARV; it is one data point, possibly the best house on the street. On the example house an ARV of $340,000 instead of $320,000 adds $20,000 to the expected profit that never existed.

Fix: use 3–5 recent sales of similar size, age and condition, work out the price per square foot of each, and take the low, the median and the high as three ARVs: conservative, base and aggressive. How to calculate ARV walks through the comp selection. In the app the deal is run at all three ARVs side by side, and with fewer than three comps the ARV part of the deal score reads "not enough data" instead of a number.

2. No contingency

Something in every house is hidden behind drywall, under a floor or inside a wall. A budget with no contingency is a budget that will be wrong by the first week.

Fix: add a contingency line, a reserve on top of the rehab estimate. The app's default is 10% of repairs: on the example house $4,800, bringing the rehab line to $52,800. It is a rule of thumb; an older house, a house you could not fully walk, or a first project where your estimates have no track record justify more.

3. Using $ per square foot as the estimate

A per-square-foot figure is a filter, not an estimate. The app's starter ranges (labelled "Starter estimate — not market data") put a medium rehab at $25–35–45 per sq ft. On 1,600 sq ft that is $40,000 to $72,000. The $32,000 between the ends of that range is almost the whole profit of the deal.

Fix: walk the house and price the work by zone and item: roof, kitchen, baths, electrical, plumbing, HVAC and so on. The square-foot range tells you which bracket you are in; the walk tells you the number.

4. Skipping zones during the walk-through

Beginners photograph the kitchen and the baths and forget the attic, the crawl space, the panel and the water heater. The expensive surprises live in the zones nobody photographed: roof, foundation, electrical, plumbing, HVAC.

Fix: walk every zone with a fixed list and take photos and notes per zone, so a zone you could not enter is marked as not seen rather than silently assumed fine. The walk-through checklist lists twelve zones. In Flip Investor OS the walk-through is twelve zones on a phone with photos and notes per zone; the field AI describes what is visible, what is possible and what cannot be verified from a photo, and it never prices anything.

5. Guessing an unknown as $0

A line you could not price (the sewer line nobody scoped, the roof seen only from the street) tends to be left blank, and a blank in a sum is a zero. The total looks complete and is not.

Fix: write "unknown" and treat the total as incomplete until every line has a number. In Flip Investor OS an unknown cost is Unpriced, never $0, and a result with unpriced lines is shown as Incomplete with a count of what is missing.

Mistakes in the costs around the rehab

6. No holding-cost line

Every month you own the house costs money: property taxes, insurance, utilities, HOA dues if any, loan interest. Six months of a modest $1,500 a month is $9,000; three months of delay adds $4,500 more.

Fix: put holding costs in the calculation as a monthly figure times the months you expect, and stress the deal at three more months. The holding costs article breaks down what goes in the monthly figure.

Holding per month = utilities + HOA + loan interest + other + (taxes + insurance) ÷ 12

7. Ignoring the cost of hard money

Hard money (a short-term loan from a private lender, priced on the property rather than on your credit) is not free money. On the example house with the app's default terms — 90% of price plus 100% of the rehab financed, 11% a year, 2 points, 6 months — the loan is $232,800 (90% of $200,000 plus the $52,800 rehab line), the points are $4,656 and the interest is $12,804, counted on the full loan for the whole term as the app's stated simplification. That is $17,460 of profit gone.

Fix: run the deal with and without financing and look at both profit and cash needed, with the points and the interest on their own lines.

8. Forgetting selling costs

The sale price is not what you keep. Agent commissions and seller closing costs on a $320,000 sale at the app's default 6% are $19,200. Beginners who skip this line think they have a $54,200 deal and find out at closing they had a $35,000 one.

Fix: always subtract selling costs as a share of ARV, and let the deal calculation do it, not your memory.

What the example house looks like with every cost counted

The figures are an example; costs vary by market and by year. What does not vary is that the three lines beginners skip (contingency, holding, selling) come to $33,000 here, almost exactly the cash profit.

Mistakes during the project

9. Change orders without a reason, and no frozen original plan

The second month of a rehab is when the plan quietly drifts: a nicer tile here, a wall moved there, a "while we're at it" in every room. If the original plan is in the same spreadsheet cell you keep editing, by the sale you cannot tell what you planned from what you did.

Fix: freeze the original plan on the day you buy and keep three sets of figures: the original, the current forecast and the actual. Every change to a budget line gets a reason written next to it. In the app the original plan is frozen when the project is created (the database refuses changes to it), the forecast and the actual sit next to it line by line, and each line carries "what changed and why". Expenses come in with a photo of the receipt that the AI reads and you confirm.

10. Deciding on a feeling instead of the margin

"It feels like a good deal" is how beginners buy at $225,000 a house whose numbers stop at $202,900. The feeling is usually the asking price, the agent's enthusiasm or the fear of losing it.

Fix: decide on two things you can check: the margin of safety and the quality of the data behind it. Work out the maximum offer, the highest price at which the profit still equals your target with every cost counted; on the example house at a 10%-of-ARV target and a cash purchase that is $202,900, while the 70% rule gives a rougher $176,000. Then stress it: ARV 5% lower, rehab 20% higher, three more months. Flip Investor OS shows the maximum offer, the stress tests and a deal score that describes margin of safety and data quality with neutral labels; it never says buy or don't buy, and neither should anyone else. You can open the free calculators and run your own house through the same arithmetic without a card.

A short checklist for the first flip

• Three to five comps, three ARVs.
• Rehab priced by zone and item after walking every zone; unknowns stay unknown.
• Contingency on top of the rehab (about 10% as a starting rule of thumb).
• Purchase closing costs, holding costs per month, financing costs and selling costs each on their own line.
• A maximum offer worked out from the numbers before you look at the asking price.
• The original plan frozen at purchase; forecast and actual tracked next to it, with a reason for each change.
• A decision made on the margin and the data, not on the feeling.

None of this makes a flip safe, and no app or spreadsheet can. It makes the risk visible before the money is spent, which is the only moment it is cheap to change your mind.