Cap rate is a ratio, not a verdict. In income-capitalization appraisal it is net operating income divided by price or value. The arithmetic is short. The fight is about which income and which price you are allowed to put in it, and about the fact that the ratio does not know your loan.
A listing that prints one number called “the cap” has already chosen a rent and an expense policy. Your job is to rebuild both from documents, then decide whether that yield is the yield you would actually buy.
The identity, and what it refuses to include
Cap rate = net operating income ÷ price (or the value you are testing).
Net operating income is what the property earns from operations in a year after operating expenses, and before mortgage payments, depreciation, and income tax. That exclusion is the point. Two buyers with different loans can look at the same cap rate and have completely different cash in the account. If you want the loan in the picture, you want cash-on-cash or a coverage ratio, which are later steps. Definitions that match this site’s calculators live in the glossary. The mortgage calculator is where principal and interest enter, and it labels its shortcuts.
Rearranged, the same identity estimates a value: value = net operating income ÷ a cap rate you are willing to defend. You may use that only when the cap rate comes from sales of similar buildings whose income you actually know. A national “average cap rate” you saw in a headline is not that evidence. If you do not have the comparable sales and their operating statements, say so, and stop short of a fake value.
How to build the income without borrowing the brochure
Start from rent the building collects, not rent the flyer hopes for.
Gross potential rent is every unit at the rent you can support with leases or with leased comps, for a full year. Then subtract vacancy and credit loss that belong to this building. A national placeholder is not a history. If the seller will not show a rent roll, you do not yet have income. Other income — laundry, parking, pet rent, storage — counts only when it shows up in deposits or a contract, not when the agent says “tenants usually pay.”
Effective gross income is what remains. Operating expenses come off next: property taxes, insurance, utilities the owner pays, repairs and maintenance, landscaping and snow if you promised them, HOA or landlord-license fees, management, and legal or accounting costs tied to the property. The expense-stack guide is the worksheet. The on-site Deal Analyzer and several other calculators subtract about 1.5 percent of price per year as a blended stand-in for taxes, insurance, and maintenance. That plug is a screen this site discloses. It is not an operating statement, and a cap rate built on it is a screen too.
Capital projects are the argument people hide. A strict net operating income often keeps the roof, the boiler, and the long-cycle flooring out of the expense line and in a reserve you still have to fund. If you leave the reserve at zero because “cap rate doesn’t include capex,” you have improved the ratio by ignoring the bill. Underwrite the reserve even when you show the ratio both ways: with it, and without it, labeled.
Debt service does not come off. Depreciation does not come off. Your personal tax bracket does not come off. If a spreadsheet arrives with those already removed, it is not net operating income, and dividing it by price will not produce a cap rate you can compare with anyone else’s.
In-place income versus a story about next year
Sellers like a pro forma: rents raised to “market,” vacancy set to a wish, management omitted because the new owner will “do it themselves.” In-place income is the leases and the trailing expenses. A ratio built on the story is a different property from the one under contract.
Ask for the rent roll, the leases, and a trailing twelve months of income and expenses. Match deposits to the rent roll if you can. Replace the tax line with the tax you will pay after the sale, because many counties reassess on a transfer and the seller’s bill is a historical document. Replace the insurance line with a quote on this address, including wind, hail, or flood if the carrier requires them. A deductible large enough to be a capital event belongs in the reserve conversation, not inside a cheerful premium.
Then compute the ratio twice and name them. One uses in-place rent and quoted expenses. One uses only the changes you can document — a signed lease at a new rent, a bid you have accepted, a tax estimate from the assessor. Anything else is a scenario, and scenarios go in the scenario simulator labeled as assumptions, not in the sentence where you tell yourself what the building “trades at.”
Why a higher ratio is not automatically a better buy
Cap rate is a price of risk and of expected income, in one year’s snapshot. A higher ratio means more income per dollar of price, or a lower price per dollar of income. It does not tell you why. Older buildings, thinner tenant demand, harder insurance, and short leases can all push the ratio up because buyers demand compensation. A lower ratio can mean a building people trust, or it can mean you overpaid for a story. You cannot read the reason off the quotient.
Compare the ratio only with sales you can actually describe: similar unit count, similar condition, similar expense burden, close enough in time that insurance and taxes have not changed regime. If the only “comp” is a listing that is not sold, you have an asking cap rate, which is an advertisement.
The ratio also ignores the buyer you will need later. A building that only appeals to the next person who believes the same pro forma is a thin exit. The pre-offer checklist asks who buys this from you. Cap rate does not.
Where careful people still fool themselves
They use the asking price in the denominator and a rent the unit has never achieved in the numerator. They drop management because they plan to self-manage, then compare the result with sales where every buyer assumed a manager. They treat one good year of occupancy as the stabilized year. They capitalize a number that still includes the mortgage and call it a cap rate anyway.
They also forget the loan on purpose and then feel betrayed by the payment. Cap rate was never the cash-flow test. After the income is honest, cash flow is what remains after debt service, and cash-on-cash relates that remainder to the cash you actually put in. Work the income first on the underwriting guide. Add the loan second. If the unlevered yield is thin and the payment is not, leverage is a cost you are choosing, not a machine that creates return.
A single year also says nothing about a lease that ends in April, a tax abatement that ends in December, or a roof the inspector dated to the year you were in school. Those facts change next year’s income. The ratio you quote should say which year it belongs to.
A sequence you can repeat without a template
Collect the rent roll and the leases. Build vacancy from this property’s history. Add only other income you can tie to a deposit or a contract. Subtract taxes at the post-sale estimate, insurance at a quote, and every operating bill the owner pays. Decide, in writing, whether the capital reserve is inside the expenses or beside the ratio. Divide by the price you would actually pay, not by a value you hoped an appraiser would invent. Write down the comparable sales you used if you are going the other direction and solving for value. If you cannot name them, you are not valuing. You are rearranging a formula.
Then ask whether you would still want the building if the loan fell through and you had to hold it with the income you just calculated. That question is the one cap rate is for.
This is education about a ratio, not a recommendation to buy at any particular yield. Appraisal practice, lender overlays, and tax rules are local and current; the documents beat the formula.
Field notes
You already know the formula if you opened this URL. The live issue is the NOI: in-place versus pro forma, whether capital spending is pretending to be a repair, and whether the price in the denominator is the price you would actually pay. A ratio built on next year's hoped-for rent describes a different building from the lease that exists.
Cap rate also does not know your loan. That is the point. Use cash-on-cash after you trust NOI. The order of documents is the underwriting guide.