Most people freeze at the first listing they take seriously. They stare at the price, the photos, the phrase “great investment opportunity,” and they have no idea whether the numbers actually work. So they do one of two things. They talk themselves into it because they like the kitchen, or they talk themselves out of it because the whole thing feels like a math test they never studied for.
Here is the truth after years of buying, managing, and walking away from deals across Utah and California, with teams that now oversee hundreds of units: you do not need a finance degree. You need five numbers and a repeatable order to run them in. Once you know the order, you can screen almost any listing in under fifteen minutes and know whether it deserves a real look or a polite goodbye.
This is the framework I hand to beginners on my teams. It is not fancy. It is fast, honest, and it protects you from the two most expensive words in real estate: “I assumed.”
Start With the Only Question That Matters
Before any spreadsheet, ask one thing. Does this property make money after everything, or does it quietly cost me money every month while I hope for appreciation?
Hope is not a strategy. Appreciation is a bonus, not a plan. So we build the number from the ground up, and we let it tell us the answer.
You are going to walk down a ladder. Each rung subtracts something real. What survives at the bottom is your cash flow, and cash flow is what keeps you in the game long enough for the appreciation to ever matter.
The Five Numbers, In Order
1. Gross scheduled rent. This is what the property collects in a full year if every unit is rented at market rate, twelve months, no gaps. If a duplex rents for $1,500 per side, that is $3,000 per month, or $36,000 per year. Do not use the seller’s dream rent. Use what comparable units actually rent for right now. If you cannot verify it, you do not know it.
2. Vacancy allowance. Nobody stays rented one hundred percent of the time. Tenants move, units sit, turnovers take a week. I plan for vacancy even in a tight market, because the market that is tight today loosens the month you sign. A common screen is 5 to 8 percent of gross rent. In a softer submarket, use more. Subtract that from gross scheduled rent and you have effective rent, which is closer to reality.
3. Operating expenses. This is where beginners get hurt, because they forget the boring costs: property taxes, insurance, repairs, maintenance, property management, trash, water, capital reserves for the roof and the water heater that will absolutely fail someday. Adding these line by line is the accurate way. But for a fast screen, use the 50 percent rule.
The 50 percent rule is a rule of thumb, not a law. It says that over time, operating expenses (not including the mortgage) tend to eat roughly half of your effective rent. It is rough. On a newer building with low taxes it may be generous. On an older building with high turnover it may be optimistic. But for a fifteen minute screen, it keeps you honest and it keeps you from fantasizing. Verify the real numbers before you ever write an offer.
4. Net operating income (NOI). Take your effective rent and subtract operating expenses. What is left is your net operating income. This is the number that describes the property itself, before any loan. NOI is the heartbeat of the deal. Two investors can look at the same building and get very different returns depending on how they finance it, but NOI does not care who owns it. It is the property’s honest earning power.
5. Debt service and cash flow. Now subtract your mortgage payment, principal and interest, for the year. What remains is your annual cash flow. Divide by twelve and you have your monthly cash flow. This is the number that hits your account. If it is positive, the property pays you to own it. If it is negative, you are paying for the privilege, and you had better have a very good reason.
Two Ratios That Tell You If the Price Is Fair
Cash flow tells you if the deal feeds you. The next two numbers tell you whether you are paying a fair price and using your money well.
Cap rate. Take your NOI and divide it by the purchase price. That is your capitalization rate, expressed as a percent. Cap rate answers a simple question: if you paid all cash, what return would the property throw off in year one? It is also how you compare a fourplex in one city to a fourplex in another. A 4 percent cap and a 7 percent cap are two very different animals, and cap rate lets you see it instantly. Lower cap usually means a pricier, safer, more appreciation-driven market. Higher cap usually means more cash flow and more risk or more work.
Cash-on-cash return. This one is personal. Take your annual cash flow and divide it by the actual cash you put into the deal: down payment, closing costs, and any money spent to make it rentable. Cash-on-cash tells you how hard your actual dollars are working. You can have a modest cap rate and a strong cash-on-cash return because a loan is doing part of the lifting. This is the number I care about most as an operator, because it measures my money, not the property’s abstract value.
The 1 Percent Rule, and Why I Do Not Worship It
You will hear the 1 percent rule constantly. It says monthly rent should be at least 1 percent of the purchase price. A $250,000 property should rent for $2,500 a month to pass.
It is a fine napkin screen. It is a fast filter for a large list. But let me be direct, because I promised you honesty: in appreciating markets like much of Utah and coastal California, the 1 percent rule almost never holds anymore. Prices have climbed faster than rents for years. If you throw out every property that fails the 1 percent test in those markets, you will throw out nearly everything, including deals that cash flow modestly today and build serious equity over time.
So use it as a first-pass sorter on a big list, not as a verdict. A property can fail the 1 percent rule and still be a smart buy if the cash-on-cash works and the location is strong. And a property can pass the 1 percent rule and still be a disaster, which brings me to the part beginners skip.
Red Flags That Kill a Deal on Sight
Some things make me stop reading before I ever open a calculator. These are not deal points to negotiate. They are exits.
- Rents that only work “after renovation” with no plan or budget. Pro forma rent is a wish. If the numbers only work in an imagined future, the deal does not work today.
- Deferred maintenance hiding in the photos. A roof at the end of its life, a foundation crack, aluminum wiring, a failing sewer line. One of these can erase two years of cash flow in a single afternoon.
- A location with declining population, closing employers, or no job base. You are betting on tenant demand. Bet where people are moving to, not away from.
- HOA or special assessment surprises. A cheap condo with a broke HOA is not cheap. It is a bill you have not read yet.
- A seller who will not share real numbers. Actual leases, actual expenses, actual tax bills. If the story keeps changing, the story is the problem.
- Cash flow that is only positive if nothing ever breaks. Something always breaks. Build the reserve in, and if the deal cannot survive one bad month, it is too thin.
If any of these show up, I do not spend the fifteen minutes. I move on. There is always another listing. There is not always another $50,000.
A Clean Worked Example (Hypothetical Numbers)
Let me run one all the way through so you can see the ladder in motion. Every number here is hypothetical and illustrative only. Yours will differ.
Say a duplex is listed at $300,000. Each side rents for $1,500 a month.
- Gross scheduled rent: $3,000 per month times 12 equals $36,000 per year.
- Vacancy allowance at 7 percent: minus $2,520. Effective rent equals $33,480.
- Operating expenses using the 50 percent rule: minus $16,740. (This is a screen. Verify the real number before offering.)
- Net operating income: $33,480 minus $16,740 equals $16,740.
- Cap rate: $16,740 divided by $300,000 equals 5.6 percent.
Now the financing. Say you put 25 percent down, which is $75,000, and finance $225,000. Assume a mortgage of principal and interest around $1,450 a month, or $17,400 a year.
- Annual cash flow: $16,740 minus $17,400 equals negative $660. That is roughly negative $55 a month.
Read that honestly. At these hypothetical numbers, the deal barely bleeds. It does not pass. Now watch what changes it. If you negotiate the price down, or the real operating expenses come in under 50 percent, or rents are actually $1,600 a side, the whole picture flips positive. That is the point of the framework. It shows you exactly which lever to pull, instead of leaving you with a vague bad feeling.
And the cash-on-cash: with negative cash flow, it is negative, so this one is a pass at this price. If you got the price to $275,000 and cash flow turned to positive $3,000 a year on $70,000 invested, your cash-on-cash would be about 4.3 percent, and now we can talk.
If running these numbers by hand feels slow the first few times, that is normal. I built a free calculator that walks the same ladder for you, so you can plug in a listing and see cash flow, cap rate, and cash-on-cash in seconds. Use it to screen fast, then do the real math on the few that survive.
How I Personally Decide Yes or No
After the numbers, I sit with three questions, and this is where being an operator, an investor, a woman of faith, and a mother all show up in the same decision.
Does it cash flow honestly, with reserves built in, at conservative assumptions? Not in the best case. In the plain case. If it only works when everything goes right, the answer is no.
Would I be at peace owning it through a hard year? Vacancy, a bad tenant, a surprise repair. If a rough season would sink me, the deal is too tight or too big for where I am. Stewardship means I do not risk what I cannot afford to lose, and I do not stake my family’s stability on a spreadsheet’s best mood.
Does it move me toward the portfolio I am actually building? A fine deal in the wrong direction is still the wrong deal. I would rather pass on a good property than lose focus.
If all three land as yes, I go deeper: real leases, real inspections, real financing quotes. The fifteen minute screen never decides the purchase. It decides what earns my next hour. That is the entire job of a fast framework. It protects your time and your capital by killing the wrong deals quickly, so the right ones get everything you have.
One honest note before you run to the listings. This is how I think and how I train my teams, but it is not financial, tax, or legal advice. Every market, loan, and tax situation is different, and yours is yours. Run your real numbers, and bring in a qualified professional, a lender, an accountant, an attorney, before you sign anything.
Keep Going
If this way of thinking clicks for you, I go deeper every week in Operator’s Notes, my newsletter where I share the real numbers, the near misses, and the frameworks I use to run the portfolio. And on The Broker’s Table podcast, I sit down with operators and investors to pull back the curtain on how deals actually get done, the good and the ugly.
Come learn with me. The best time to get fluent in these numbers was your first deal. The second best time is the next listing you open.
