The definition, and the one line that ruins it
Net operating income is effective gross income minus operating expenses. Effective gross income is all the money the property collects after an allowance for vacancy and uncollected rent. Operating expenses are what it costs to run the building: taxes, insurance, management, repairs, owner-paid utilities, association fees, the licence, the lawn.
What is deliberately excluded is debt service — the mortgage payment, both the interest and the principal — and capital expenditure. Income tax is out too, and so is depreciation, which is an accounting entry rather than a cash cost. Cap rate is then NOI divided by price.
The exclusion of the loan is the whole design. A building has one NOI. It has as many cash-on-cash returns as there are ways to finance it. If you subtract a mortgage payment before dividing by price, you have produced a number that changes when the buyer changes, which defeats the purpose of a measure whose only job is to let two buildings be lined up next to each other. This is the single most common error in the field and it is usually made in good faith, by someone who reasons that the mortgage is obviously a cost of owning the property. It is a cost of owning it. It is not a cost of operating it.
Capital expenditure, and the honest awkwardness there
Capital expenditure — the roof, the furnace, the repipe — is excluded from NOI by convention, and that convention is genuinely defensible: capital items are irregular, they extend the life of the asset rather than maintaining it, and including a made-up annual figure would make cap rates incomparable again since every analyst would pick a different figure.
It is also the reason quoted cap rates flatter properties. The roof is real. Excluding it from the comparison measure does not make it stop being real, it just means the comparison measure is not the number you should be spending. This page shows both: the cap rate as conventionally built, so it lines up against what brokers quote, and the cap rate after a reserve, so you can see what the building actually throws off. The gap between them is often half a percentage point or more, which on a cap rate of six is a large fraction of the whole. The reserve calculator builds that annual figure from the actual components rather than a guess.
Cap rate as a valuation lever
Run the equation backwards and it prices things. If comparable buildings trade at a 6.5 percent cap rate, then value equals NOI divided by 0.065, which means every dollar of annual NOI carries about 15.4 dollars of value. Cut $1,000 a year of expense and you have not saved $1,000, you have created roughly $15,400 of value on paper, provided a buyer accepts the same cap rate.
| Market cap rate | Value per $1 of annual NOI | Value of $1,000/yr saved |
|---|---|---|
| 4% | $25.00 | $25,000 |
| 5% | $20.00 | $20,000 |
| 6% | $16.67 | $16,670 |
| 7% | $14.29 | $14,290 |
| 8% | $12.50 | $12,500 |
| 10% | $10.00 | $10,000 |
Two cautions come with that table. The first is that it is only as good as the cap rate you feed it, and cap rates for small residential properties are frequently inferred from very few genuine comparables. The second is that it cuts both ways: at a low cap rate, a small deterioration in NOI removes a startling amount of value, which is the mechanism behind a lot of losses that get described afterwards as market movement.
Where the number comes from and where it stops
A cap rate is not a return you receive. Nothing pays you 6.5 percent because the cap rate is 6.5 percent. It is a ratio between a year of operating income and a price, and it is useful precisely because it is narrow. What you actually receive depends on the loan, which is the cash-on-cash question, and on whether the income holds, which is the stress test question.
Nothing here should be read as a statement about what cap rate is good, achievable or normal, because that is entirely a function of market, asset class, condition and moment, and any figure written down here would be wrong somewhere and out of date everywhere. Nor does the page touch tax: how expenses are classified, what is deductible, how depreciation works and what happens on a sale are matters for a CPA and depend on federal rules, your state and the entity that owns the property. If you are moving from owning a home to owning a rental, the home buying steps guide covers the parts of a purchase that are the same either way.
Questions people ask
Should the mortgage payment ever go into NOI?
No. Not the interest, not the principal, not the escrowed portion of taxes and insurance as a bundle. Taxes and insurance are operating expenses and belong in NOI on their own lines, entered as annual amounts rather than as part of a monthly escrow payment — that split is where the mistake usually creeps in, because the lender presents one number. If you want the figure that includes the loan, that is cash flow, and it is a different measure answering a different question. Keep the two separate and both stay useful.
Why does my cap rate look different from the one on the listing?
Usually because of what was left out of the listing version. Common omissions are management valued at zero on the assumption the buyer self-manages, vacancy set to zero on a currently occupied unit, property tax quoted at the seller's current assessment rather than what a sale would trigger, and maintenance omitted entirely. Any one of those can move a cap rate by a full point. Rebuild the expenses from your own figures and compare like with like — that is the only version of the comparison that means anything.
Is the capital reserve an operating expense or not?
By the conventional definition, no, and that is why this page keeps it out of the headline NOI. Capital expenditure replaces or extends the life of a component rather than maintaining current operation, which is a distinction that matters both to how the industry quotes cap rates and, separately and with different rules, to how expenditure is treated for tax. The tax treatment specifically is not something to take from a calculator: the boundary between a repair and an improvement has real consequences and depends on federal rules and your circumstances. Ask a CPA. For comparing buildings, follow the convention. For deciding what you can spend, use the after-reserve figure this page also shows.
What is the gross rent multiplier for?
Screening, and nothing more. It is the price divided by annual gross rent, so it ignores every expense and every vacancy. Its only virtue is that it needs two numbers you can get from a listing in five seconds, which makes it useful for discarding obviously unworkable properties quickly. It is worthless for comparing two properties with different tax rates, different utility arrangements or different management structures, which is to say almost any two real properties. Use it to sort a list. Never use it to decide.
Does a higher cap rate mean a better property?
It means a higher ratio of income to price, and this page will not tell you whether that is good. Higher ratios and higher risk tend to travel together for reasons that are not mysterious — condition, location, tenant stability, how likely the income is to still be there in five years. A lower ratio can reflect a market where buyers are confident about the income continuing. Neither is a verdict, and treating any particular figure as a target is how people end up buying the thing the ratio was warning them about.