9 Mistakes That Make a Bad Rental Deal Look Good
Almost every deal that disappoints was modelled optimistically in one of these nine specific places.
+$266 → −$194
The same deal per month, once vacancy, maintenance, CapEx and management are added.
The demonstration
Take an ordinary-looking deal: a $260,000 house renting for $2,000 a month, 20% down at 7.0% on a 30-year loan. Here is the analysis most people do in their head, next to the one the property will actually perform.
The napkin version
- Rent
- $2,000
- Principal + interest
- −$1,384
- Property taxes
- −$250
- Insurance
- −$100
“$266 a month in cash flow.”
The honest version — same property
- Napkin cash flow
- $266
- Vacancy @ 5%
- −$100
- Maintenance @ 5%
- −$100
- CapEx reserve @ 5%
- −$100
- Property management @ 8%
- −$160
−$194 a month. The deal loses money.
Nothing exotic happened there. No disaster, no bad tenant, no rate shock — just four ordinary lines that the napkin version left out. Add the ~$8,000 of closing costs to the $52,000 down payment and the deal’s cash-on-cash return is about −3.9%.
The nine mistakes
| # | Mistake | Typical effect on the answer |
|---|---|---|
| 1 | Zero or token vacancy | Overstates income by 4–8% of gross rent, every year. |
| 2 | No CapEx reserve | The largest single omission. Understates true expenses by 5–15% of rent. |
| 3 | Self-management counted as free | Overstates NOI by 8–12% of rent and hides the cost of your own time. |
| 4 | Using the seller’s expense numbers | Taxes reassess, insurance reprices, and their management deal is not yours. |
| 5 | Closing costs and rehab left out of cash invested | Overstates cash-on-cash by 10–30%. |
| 6 | Calling rent-minus-mortgage “cash flow” | The single most common error. It is not cash flow; it is a subtraction. |
| 7 | Pro forma rent instead of market rent | Turns a rent forecast into an income statement. |
| 8 | Ignoring the rate reset or assuming a refinance | Models a loan you have, using a payment you hope for. |
| 9 | Counting appreciation as return | Converts a forecast into a number people spend. |
The three that matter most
1. No CapEx reserve
Maintenance is fixing the disposal. CapEx is the roof, the furnace, the water heater, the windows, the kitchen. They are different lines because they behave differently: maintenance is small and frequent, CapEx is large and rare. A property that has produced $200 a month for four years and then needs a $14,000 roof produced roughly $50 a month.
Most people plug 5% of rent and move on. Budget it component by component — replacement cost divided by remaining life — and the honest number is usually two to three times that. On the $240,000 example used across these guides, component-based CapEx comes to about $335 a month against a 5% plug of $105. That single line is the difference between a deal that works and one that does not: how much to budget for CapEx.
2. Your labour is not free
Self-managing saves cash, not cost. Two arguments for modelling the management fee anyway, both practical rather than moral. First, the property must survive you — a new job, a move, an illness, or simply losing interest. Second, when you sell, the buyer prices the property on a managed NOI, so a self-managed pro forma is a return you cannot transfer.
If you genuinely want credit for your labour, the clean way is to model the fee in the expense line and count the saved fee as separate income for the job you are doing. That keeps the property’s performance and your wage from being blended into one flattering number. See property management fees.
3. Cash flow is not rent minus mortgage
This is mistake 6, and it is the one that produces the widest gap between expectation and reality. The correct sequence is: gross scheduled rent → subtract vacancy → subtract all operating expenses to get NOI → subtract debt service → cash flow. Skipping the middle step is what turns −$194 into $266.
The other six, briefly
How to stop making them
Not by being more careful — by using the same structure every time so the lines cannot be forgotten. Whether that is a template spreadsheet or a tool, the value is identical: the vacancy, maintenance, CapEx and management fields are there, and leaving one at zero is a visible choice rather than an oversight. The free calculator defaults all four to realistic non-zero values for exactly this reason — you can lower them, but you have to do it deliberately.
The second habit worth building: run every deal twice, once at your estimate and once with rent 10% lower and vacancy doubled. A deal that survives both is a deal. A deal that only works in the first version is a forecast.
Frequently asked questions
What is the most common rental property analysis mistake?
Treating rent minus the mortgage payment as cash flow. It omits vacancy, maintenance, capital reserves and management — typically 20 to 30% of gross rent — which is usually more than the entire cash flow the deal was supposed to produce.
How much should I budget for maintenance and CapEx?
As separate lines. Maintenance commonly runs 5 to 10% of gross rent for a reasonably maintained property. CapEx is better derived from component replacement costs and remaining lives, which on an ordinary single-family rental typically lands well above the 5% figure most people plug in.
Should I include property management if I self-manage?
Yes, in the property's expenses. The property has to work when you are not available to run it, and a buyer will price it on managed numbers. If you want credit for the labour, count the saved fee separately rather than deleting the expense.
Is negative cash flow always a bad deal?
Not automatically — some investors knowingly accept it in high-appreciation markets or during a value-add period. It is only a defensible choice when it is a choice: you can fund the shortfall indefinitely, and you have modelled what happens if the appreciation does not arrive.