Cap rate is a snapshot metric, not a total-return forecast. It measures a single year of stabilized income relative to the asset's price, assuming no mortgage. The formula is straightforward: Cap Rate = Net Operating Income (NOI) / Current Market Value. Expressed as a percentage, it reads: Cap Rate (%) = (NOI / Market Value) x 100. NOI itself equals all rental income collected minus operating expenses such as property taxes, insurance, maintenance, property management fees, and vacancy allowance. It does not include mortgage principal or interest, depreciation, or capital expenditures, because those vary by owner and financing structure. Stripping out financing is exactly what makes the cap rate useful: two investors with different down payments and loan terms can still agree on what a property is worth by looking at the same NOI divided by the same price.
Because cap rate and property value move in opposite directions, a rising cap rate signals a falling price or rising income, while a falling cap rate signals a rising price or falling income. Markets price assets on prevailing cap rates the way bond markets price debt on yields. In a high-demand urban market like San Francisco or Manhattan, buyers accept 3 to 4 percent cap rates because they expect appreciation to compensate for thin current yield. In secondary and tertiary markets, single-family rentals and small multifamily properties commonly trade at 6 to 9 percent cap rates, reflecting higher yield expectations and less liquidity. Neither number is inherently right or wrong; the relevant question is always whether the cap rate is appropriate for the local market, the asset class, and the condition of the property.
Cap rate has real limitations that every landlord and investor should understand before relying on it. It assumes a fully stabilized, market-rate occupancy level, which may not reflect a property in lease-up or one with deferred maintenance that is temporarily underrented. It also ignores financing entirely, so a cash buyer and a leveraged buyer will experience very different actual returns even at identical cap rates. For a fuller picture of how leverage changes the deal, pair cap rate analysis with cash-on-cash return, which divides annual pre-tax cash flow after debt service by the actual cash invested. Use cap rate to screen and compare; use cash-on-cash to stress-test what the deal actually puts in your pocket.
Worked example
A fourplex in Phoenix generates $72,000 in gross annual rent. After accounting for a 5 percent vacancy allowance ($3,600), property taxes ($6,000), insurance ($2,400), maintenance ($4,800), and a property management fee of 8 percent of collected rent ($5,472), total operating expenses come to $22,272. NOI = $72,000 - $3,600 - $22,272 = $46,128. The seller is asking $650,000. Cap Rate = $46,128 / $650,000 = 7.1 percent. A competing fourplex down the street lists for $720,000 with an identical NOI. Its cap rate = $46,128 / $720,000 = 6.4 percent. All else being equal, the first property offers a better current yield. If comparable fourplexes in that Phoenix submarket are trading at 6.5 to 7.5 percent cap rates, both deals are in the normal range, but the first sits closer to the favorable end of that band.