How to Calculate Cap Rate

Most people reaching for a cap rate calculator assume the hard part is the division. It is not. The division is two keystrokes. The hard part is the two numbers you feed into it, and most first-timers get both of them wrong because they copy the listing's rent and the tax bill without adjusting anything. The actual question of how to calculate cap rate on a real deal is a question of what to count and what to throw out, not a question of arithmetic. A defensible cap rate calculation requires four inputs, using a single-family rental and a fourplex as examples, so you can do the calculation yourself before you make an offer.

Why the listing rent is not your starting point

You do not start with the asking rent. You start with gross potential rent, which is what the property would collect in a full year if every unit were occupied at market rent, not at the in-place rent and not at the landlord's claimed rent. Market rent means what a willing, unpressured tenant would pay today for that unit in that building. If the current tenant is paying $1,200 and the market is $1,400, you use $1,400. If the owner is asking $1,600 and the market is $1,400, you use $1,400. The cap rate formula real estate investors use is a forward-looking stabilized measure, and a below-market lease is a temporary condition, not a permanent feature of the asset.

Once you have gross potential rent, you subtract money you will not collect. That is vacancy and credit loss, which covers empty units, tenants who skip out, and units that sit dark between tenants. The rule is to use a market-based vacancy rate, not the current vacancy of the subject property. If the building is full today, that is good news, but it does not mean you should assume 0% vacancy forever. A typical stabilized vacancy allowance for residential is 5% to 10% of gross potential rent, depending on the market. For a cap rate calculation example, use 5% if the market is tight and 10% if it is soft. The result after this deduction is effective gross income, the number you actually build your NOI on.

Operating expenses are the recurring costs to keep the property running and rentable. They include property taxes, insurance, utilities you pay, maintenance and repairs, property management fees, HOA fees, and trash removal. They do not include mortgage payments, because debt service is financing, not operations, and they do not include capital expenditures like a new roof or a replacement furnace, because those are improvements to the asset, not costs of running it. The most common mistake in the cap rate formula real estate world is to include the mortgage and exclude the roof. Both are wrong. A good rule of thumb: if the cost keeps the property in its current condition, it is an operating expense; if it extends the life of the building, it is not.

Now you subtract operating expenses from effective gross income. That gives you net operating income, the numerator of your cap rate. Then you divide NOI by the current market value of the property, not by the asking price and not by what you hope to pay. The cap rate formula is NOI divided by current market value, and the alternative version uses purchase price, which is the same thing on the day you close. Multiply by 100 to get a percentage. If NOI is $18,500 and value is $250,000, the cap rate is 7.4%. That is the number that tells you the unlevered yield of the asset before debt, before income tax, and before any growth. It is a snapshot of this year's income, not a forecast of your return.

Here is the cap rate calculation example, kept because it is right. A single-family rental has gross annual rent of $30,000. Apply a 5% vacancy allowance, which is $1,500, leaving effective gross income of $28,500. Operating expenses total $11,500, covering property taxes of $4,000, insurance of $1,500, maintenance of $2,500, property management of $2,000, and vacancy-related costs of $1,500. NOI is $28,500 minus $11,500, which equals $17,000. If the property's current market value is $230,000, then cap rate equals $17,000 divided by $230,000, which is 7.4%. A 7.4% cap rate is a moderate yield for a single-family home in an average location, and it tells you the property returns 7.4% of its value each year before financing.

Now the fourplex, because the numbers scale and the expenses behave differently. Gross annual rent is $72,000, which is $1,500 per unit times four units times twelve months. Use a 7% vacancy allowance, which is $5,040, leaving effective gross income of $66,960. Operating expenses are higher per unit for a multi-tenant building: property taxes of $9,000, insurance of $4,500, utilities of $3,600, maintenance of $4,000, property management of $5,760, and vacancy costs of $2,260, totaling $29,120. NOI is $66,960 minus $29,120, which equals $37,840. If the asking price is $530,000, then cap rate equals $37,840 divided by $530,000, which is 7.15%. The cap rate is close to the single-family example because the higher income is offset by higher operating expenses, which is exactly the trade-off you should expect.

Before you trust your number, correct the three failures that make a cap rate calculation example useless. First, never use trailing NOI without adjusting for a one-time repair or a non-market rent. If the roof was replaced last year and the landlord counted it as an expense, that is capital, not operating, and your NOI is too low. If a tenant has been in place for a decade and pays below market, your NOI is too low for valuation and too high for cash flow. Second, never include debt service. The cap rate is an unlevered metric; it measures the property, not your financing. Third, never use a vacancy rate of zero because the building is full today. The cap rate assumes a stabilized year, not the luckiest month.

The cap rate formula real estate investors rely on is a direct capitalization tool, and it has a sibling called the gross rent multiplier that you will see on every listing site. The GRM is price divided by gross annual income, and it ignores operating expenses entirely. That makes it useless for comparing a net-leased asset, where the tenant pays the costs, to a gross-leased one, where the landlord does. The cap rate, by contrast, normalizes for expense structure, which is why it is the standard for commercial real estate analysis and underwriting. If you are working in a spreadsheet, you can build a sensitivity table that shows how value changes with cap rate and NOI, which is what analysts use to stress-test a deal.

Cap rate is a yield, not a return. The distinction matters because the cap rate formula real estate novices memorize, NOI divided by value, only equals your total return if income never grows and the property never appreciates. In reality, total return equals cap rate plus income growth rate plus value change rate, which is why a low cap rate on a stable asset can be smarter than a high cap rate on a risky one. The high cap rate property may be high because the market expects declining rents or rising vacancy. The low cap rate property may be low because the market expects steady appreciation. Cap rate alone cannot tell you which is which; it is a snapshot of this year's income, not a forecast of your wealth.