Cash flow is effective gross income minus operating expenses minus debt service. Simple to write and easy to get wrong, because most errors live in the inputs. Assess vacancy, repairs and maintenance, capital reserves, property taxes, insurance, management, utilities, and financing terms before you trust any number a listing gives you.
The Formula
Four lines, in order.
Gross scheduled income. Every dollar the property would collect at full occupancy at market rent.
Effective gross income. Gross scheduled income minus vacancy and credit loss, plus any other income the property genuinely produces.
Net operating income. Effective gross income minus operating expenses. Operating expenses include property taxes, insurance, management, maintenance and repairs, utilities you pay, and reserves for capital items. They do not include your loan payment.
Net cash flow. Net operating income minus debt service.
That is the whole calculation. The difficulty is never the arithmetic.
Why the Inputs Break the Deal
I teach the Wealth Cycle: creating income, protecting it through entities, and investing it in income-producing assets. Real estate is a common conversion point in that cycle, and the way people lose money on it is remarkably consistent.
They use asking rent instead of achievable rent. They assume full occupancy. They budget nothing for the roof, the furnace, or the turnover between tenants. They price management at zero because they will do it themselves, without valuing their own hours. Then a normal year arrives and the number they relied on was never real.
Income called passive still needs decisions, monitoring, and care. I call it pactive. Rental property is a clear case: a vacancy, a repair, and a tenant transition all demand time, and all of them are ordinary rather than exceptional.
The Input Checklist
Define every one of these before you calculate anything. Get each from a source rather than an assumption.
| Input | What it means | Where to source it | Common error |
| Market rent | What the unit actually rents for now | Comparable leases in the same submarket, verified by a local professional | Using asking rent or a seller’s projection |
| Vacancy and credit loss | Time unoccupied plus uncollected rent | Local market data from a licensed professional | Assuming full occupancy |
| Other income | Parking, laundry, fees that genuinely recur | Verified historical statements | Counting income the property never actually collected |
| Property taxes | The assessment after any reassessment on sale | The county assessor directly | Using the seller’s current tax bill |
| Insurance | An actual quote for your ownership | A broker quote in writing | Estimating from a percentage |
| Management | Cost of managing, whether you pay it or perform it | Local management quotes | Entering zero because you will self-manage |
| Maintenance and repairs | Routine, ongoing upkeep | Historical statements and local guidance | Budgeting only for what broke last year |
| Capital reserves | Roof, systems, and other large items amortized | Age and condition of each system | Omitting it entirely |
| Utilities | Any the owner pays | Historical bills | Assuming the tenant pays everything |
| Turnover costs | Cleaning, repairs, and marketing between tenants | Local practice | Treating each turnover as free |
| Debt service | The actual payment on the actual terms offered | Your lender in writing | Using a rate you were quoted informally |
The Worked Deal
Hypothetical example. Every figure below is a placeholder for educational illustration only. No market rents, vacancy rates, expense ratios, management fees, or interest rates are asserted. The editor must replace any published figures with current data from a named primary source, or leave the structure as a template.
| Line | Base case | Higher vacancy case | Higher maintenance case |
| Gross scheduled income | [input A] | [input A] | [input A] |
| Less vacancy and credit loss | [input B] | [input B increased] | [input B] |
| Effective gross income | [A minus B] | [A minus increased B] | [A minus B] |
| Property taxes | [input C] | [input C] | [input C] |
| Insurance | [input D] | [input D] | [input D] |
| Management | [input E] | [input E] | [input E] |
| Maintenance and repairs | [input F] | [input F] | [input F increased] |
| Capital reserves | [input G] | [input G] | [input G] |
| Utilities and other | [input H] | [input H] | [input H] |
| Net operating income | [EGI minus C through H] | [recalculated] | [recalculated] |
| Debt service | [input I] | [input I] | [input I] |
| Net cash flow | [NOI minus I] | [NOI minus I] | [NOI minus I] |
The instruction that matters is not the arithmetic. It is that you build all three columns before you buy, not after.
Reading the Sensitivity
When you run the three columns with your own sourced inputs, watch for three things.
Which single variable flips the deal negative. Every property has one. Usually it is vacancy or debt service. Knowing which one tells you what to monitor.
How much cushion exists. If a modest increase in vacancy erases the whole margin, that is a thin deal regardless of how the base case reads.
What happens when two things go wrong together. Vacancy and a major repair frequently arrive in the same year, because a tenant leaving is when you discover what needs replacing.
Financing deserves separate attention. Debt service is usually the largest single line below net operating income, and terms change what an identical property produces. Two buyers, same building, different loans, different outcome.
The Boundary
I’m an educator and a wealth-education coach. Licensed professionals give regulated advice.
I’m not a CPA, an attorney, a real estate broker, or an investment adviser, and Integrated Wealth Systems does not recommend properties, markets, or transactions. Nothing here is investment, tax, or legal advice for your situation.
Depreciation, deductibility, passive activity treatment, and how rental income is characterized are all fact-specific and rule-dependent. Verify at the IRS and with a CPA. Local requirements, licensing, landlord-tenant rules, and disclosure obligations vary by jurisdiction; verify with your official state agency and an attorney.
Real estate can lose money, and leverage increases both outcomes. I make no guarantee of cash flow, appreciation, tax treatment, or any result within any period of time. Wealth is a team sport: build around people who know tax, law, business, assets, and execution, and have them review any deal before you sign.
FAQs
Does the mortgage payment go in operating expenses?
No. Operating expenses stop before financing. Debt service is subtracted after net operating income, which is what lets you compare properties independently of how each is financed.
Should I include my own labor if I self-manage?
For an honest comparison, price management at what it would cost to hire, even if you perform it. Otherwise you are comparing a property to itself with free labor attached, and that labor stops the moment your circumstances change.
What is a good cash flow number?
There is no universal threshold, and I will not publish one. What matters is whether the number survives your sensitivity cases and compensates you for the capital, risk, and hours committed.
How do I estimate capital reserves?
Work from the age and condition of each major system and amortize the replacement cost over its remaining life. An inspection report and a contractor’s input are worth more than any rule of thumb.
Do I need an entity to hold rental property?
That depends on your state, your exposure, your financing, and your tax position, which makes it a question for a business attorney and a CPA rather than a general answer.
Next Step
Take a property you are actually considering and build all three columns using sourced inputs rather than estimates. Then identify the one variable that flips it negative and decide whether you can live with that exposure. Take the completed analysis to a CPA, an attorney, and a licensed real estate professional before you make an offer. The Wealth Cycle overview and the Real Money Talks podcast cover the wider sequence.
