Two rentals can bring in the exact same rent and land in completely different places financially. The difference usually comes down to cash flow, the number that tells you what is left over after every bill gets paid, not just how much rent hit your account.
Quick Answer
Cash flow is the money left over from a rental property after collecting rent and paying every expense, including the mortgage. The formula is Net Operating Income (NOI) minus debt service (mortgage principal and interest): Cash Flow = NOI − Mortgage Payment. Positive cash flow means the property pays for itself and puts money in your pocket every month. Negative cash flow means you are covering a shortfall out of pocket. It is the single number most landlords check first, because it answers the question rent alone cannot: is this property profitable once financing is factored in.
What Is Cash Flow, Exactly?
Cash flow measures what is left over from a rental property after every expense is paid, including the mortgage. It is different from Net Operating Income (NOI), which stops before debt service. Cash flow is the number after financing costs come out too, which makes it the closest thing to “real” take-home profit on a financed property.
- Positive cash flow means rental income covers every expense, including the mortgage, with money left over.
- Negative cash flow means expenses and debt service exceed rental income, and the landlord is covering the gap from other funds.
Working with independent landlords managing everything from a single duplex to growing portfolios, we hear the same pattern come up constantly: two landlords look at properties with identical rent rolls and walk away with very different results, because one financed the deal at a rate or term the numbers could not support. Rent tells you what is coming in. Cash flow tells you what is yours.
How to Calculate Cash Flow (With a Worked Example)
The formula builds directly on NOI, so it helps to calculate that first.
| Step | Formula |
|---|---|
| 1. Net Operating Income (NOI) | Gross rental income − Operating expenses (taxes, insurance, repairs, utilities) |
| 2. Cash Flow | NOI − Mortgage payment (principal + interest) |
Worked example: A rental brings in $2,200 in monthly rent. Operating expenses (taxes, insurance, repairs, property management) run $700 a month, putting NOI at $1,500. The mortgage payment is $1,150 a month. Cash Flow = $1,500 − $1,150 = $350 a month, or $4,200 a year.
Financing terms move this number more than almost anything else. As of September 3, 2026, the average 30-year fixed mortgage rate sat at 6.71%, according to Freddie Mac’s weekly Primary Mortgage Market Survey. A rate that is even half a point higher or lower on the same loan amount can shift the monthly payment enough to flip a property from positive to negative cash flow, which is why the mortgage terms matter as much as the rent when running these numbers before a purchase.
Cash flow does not exist in isolation. It is one of four core numbers, alongside NOI, cash-on-cash return, and equity, that give a full read on how a property is performing. A rising vacancy rate hits this number directly too, since every vacant day is rent that never reaches the NOI line in the first place.
What Is a Good Cash Flow for a Rental Property?
There is no single dollar figure that applies everywhere, since purchase price, market, and financing all vary too much for one rule to fit. That said, two common rules of thumb give a useful starting point.
| Benchmark | What it says |
|---|---|
| $100-$200 per door, per month | A commonly used minimum target for a single-family or small multifamily rental after all expenses, including the mortgage |
| 1% rule (acquisition screening) | Monthly rent should be roughly 1% of purchase price for a deal to have a realistic shot at positive cash flow, used as an early screen before running full numbers |
Both are shortcuts, not guarantees. A property that clears $150 a month in cash flow but sits in a market with rising insurance costs or an aging roof can turn negative fast. The formula above, run with your actual numbers, always beats a rule of thumb.
What counts as “good” also depends on strategy. Some investors accept break-even or slightly negative cash flow in exchange for strong appreciation or equity growth in a high-demand market. Others prioritize cash flow above all else and will not buy a deal that does not clear a set dollar amount per door from day one. Neither approach is wrong, but know which one you are optimizing for before you run the numbers.
A Real-World Example
Consider a landlord like David, who owns a single-family rental in the Midwest. This is a common scenario, not a specific customer story. He collects $1,800 in monthly rent. Taxes, insurance, and a maintenance reserve run $450 a month, putting his NOI at $1,350. His mortgage payment is $1,050 a month, giving him $300 a month in positive cash flow, or $3,600 a year.
When a tenant turnover leaves the unit vacant for three weeks, David loses roughly $1,250 in rent that month, more than three months of typical cash flow in one stretch. Tracking cash flow monthly, rather than glancing at his bank balance a few times a year, is what lets him see the dip immediately and budget around it instead of being surprised by a tight month later.
Common Mistakes to Avoid
Confusing Cash Flow With Profit on Paper
A property can show positive cash flow every month and still lose money on paper once depreciation, capital expenditures, and amortization are factored in. Cash flow tells you what hits your bank account, not your full tax or accounting picture.
Leaving the Mortgage Out of the Calculation
Some landlords calculate NOI and stop there, treating it as their bottom line. Skipping the mortgage payment step overstates profitability on any financed property and can mask a deal that is really cash-flow negative.
Underestimating Vacancy and Maintenance Reserves
A cash flow projection built on 100% occupancy and zero repairs is not a real projection. Build in a vacancy allowance and a maintenance reserve before calling a number “cash flow,” not after a surprise expense wipes out three months of it.
Not Recalculating After a Rate or Term Change
Refinancing, an adjustable-rate reset, or a new insurance premium all change the mortgage payment or expense side of the formula. Landlords who calculate cash flow once at purchase and never again are working from a number that may no longer be accurate.
Cash flow is simple to calculate, but the number only stays useful if you rerun it whenever rent, expenses, or financing change. The questions below cover what landlords ask most often.
FAQ
How does cash flow work in real estate?
Cash flow works by subtracting every expense, including the mortgage, from the rental income a property collects. What remains is Cash Flow = NOI − Mortgage Payment. Positive cash flow means the property generates money after all costs; negative cash flow means the owner is covering a shortfall.
What is a good monthly cash flow for rental property?
A commonly used benchmark is $100-$200 per door, per month, after all expenses including the mortgage. The right number for you depends on your market, your financing, and whether you are prioritizing monthly income or long-term appreciation over cash flow. Treat it as a starting point, not a hard rule, since local costs vary widely.
How do I tell if a property will cash flow before buying it?
Run the full formula (NOI minus the projected mortgage payment) using realistic rent, expense, and vacancy estimates before you buy, not just after closing. The 1% rule (monthly rent near 1% of purchase price) is a fast early screen, but always confirm with the actual numbers before making an offer.
What is cash flow in simple terms?
Cash flow is what is left in your pocket after a rental property pays for itself. Rent comes in, every bill (taxes, insurance, repairs, mortgage) goes out, and whatever remains is your cash flow for that period. Positive means the property supports itself and pays you too; negative means it does not.
What’s the difference between cash flow and NOI?
NOI is income minus operating expenses only, before the mortgage. Cash flow takes that NOI figure and subtracts the mortgage payment too. A property can have strong NOI and still have thin or negative cash flow if the debt service is high.
Can a property have positive cash flow and still be a bad investment?
Yes. Positive cash flow does not account for major deferred maintenance, a declining local market, or a mortgage structure (like an adjustable rate) that could turn negative later. Cash flow is one input into a purchase decision, not the whole picture.
How can landlords improve cash flow on an existing rental?
The fastest levers are reducing vacancy, refinancing to a lower rate when the market allows it, and trimming recurring operating expenses. For a full breakdown of practical ways to increase monthly cash flow, see our rental property cash flow checklist.
Conclusion
Cash flow is the number that turns rent collected into what a landlord genuinely gets to keep. Three things to do next: calculate your current cash flow using NOI minus your mortgage payment, compare it against a realistic benchmark for your market and strategy rather than a generic rule of thumb, and recalculate any time rent, expenses, or financing terms change instead of trusting a number from months or years ago.
If you want cash flow tracked automatically alongside NOI, cash-on-cash return, and equity instead of recalculated by hand, RentRedi’s Portfolio Performance dashboard pulls rent collection, expense, and mortgage data into one live view for every property in your portfolio.