How to Calculate Cap Rate for Rental Properties Like a Pro

How to calculate cap rate for rental properties (and why most landlords get it wrong)

A friend sent me a listing last month. Duplex, $340,000, gross rents of $3,400 a month. He'd already done the math in his head — "that's a 12% cap rate, easy" — and wanted me to confirm before he made an offer. I ran the real numbers. The cap rate came out at 5.6%. He went quiet for a solid thirty seconds.

That gap between 12% and 5.6% is the whole story of this article. The formula everyone quotes is simple, almost deceivingly so. The mistakes all happen in what you decide to put into it.

The formula, and the one line everyone misreads

Cap rate expresses the unlevered return a property produces if you bought it in cash. That word — unlevered — is where most people trip.

The formula:

Cap rate = Net operating income ÷ Property value

Net operating income (NOI) is gross rental income minus operating expenses. Not minus your mortgage. Not minus your down payment. Not minus the closing costs you paid the title company. If you have a loan on the property, that loan has no business appearing anywhere in this equation.

What counts as operating expenses

Here's the list I use when I underwrite a deal. It's longer than most people expect:

• Property taxes
• Insurance (landlord policy, not a homeowner policy)
• Property management fees, typically 8–10% of collected rent
• Repairs and routine maintenance
• HOA dues, if any
• Vacancy allowance — I default to 5%, more on student or seasonal rentals
• CapEx reserve, usually 5–8% of gross rents for roofs, HVAC, flooring, water heaters
• Utilities the owner covers, lawn care, pest control, bookkeeping

Notice what's missing from that list: principal and interest. And notice what's included that most first-time calculators skip entirely — vacancy and CapEx.

Now, why does this matter so much? Because a property that looks like a 9% cap rate on paper, once you load in realistic vacancy and a CapEx reserve, often lands at 6% or below. That's the difference between a deal and a trap.

How to handle vacancy and CapEx honestly

I'll admit I ignored CapEx reserves for the first two years I owned rentals. Every deal looked great. Then a water heater died in February, the roof on another property needed patching, and I understood why the numbers had been lying to me.

Treat vacancy as a permanent line item even if your unit has been occupied for three straight years. A tenant leaves eventually. The turnover month — lost rent, cleaning, paint, a lock change — costs you roughly one month's rent every couple of years.

CapEx is the harder one because it's invisible until it isn't. A roof has a life of maybe 25 years. If the current one is 18 years old, you're buying a problem, not a house. Setting aside a fixed monthly amount smooths that out and keeps your cap rate honest.

A cap rate example, worked through step by step

Numbers beat theory. Here's a real one from a small multi-family I analyzed last year.

The inputs

• Purchase price: $250,000
• Monthly rent: $2,000, so $24,000 gross annually
• Vacancy allowance: 5% → $1,200
• Property taxes: $3,000
• Insurance: $1,400
• Property management: 9% of collected rent → roughly $2,050
• Maintenance and repairs: $1,800
• CapEx reserve: 6% of gross rent → $1,440
• Lawn care and misc: $1,110

The math

Effective gross income: $24,000 − $1,200 = $22,800

Total operating expenses: $3,000 + $1,400 + $2,050 + $1,800 + $1,440 + $1,110 = $10,800

NOI: $22,800 − $10,800 = $12,000

Cap rate: $12,000 ÷ $250,000 = 4.8%

Same property, calculated by a seller who "forgot" vacancy, management and CapEx reserves:

Line item	Optimistic view	Realistic view
Gross annual rent	$24,000	$24,000
Vacancy	$0	$1,200
Property taxes	$3,000	$3,000
Insurance	$1,400	$1,400
Management	$0 (self-managed)	$2,050
Maintenance	$600	$1,800
CapEx reserve	$0	$1,440
Other	$0	$1,110
NOI	$19,000	$12,000
Cap rate	7.6%	4.8%

Two honest people looking at the same building, two cap rates that differ by nearly three percentage points. Both of them are doing arithmetic correctly. One of them is doing it usefully.

Which calculation should you trust when you're the buyer? The conservative one. Always. If the deal still works at 4.8%, you've found something worth pursuing. If it only works at 7.6%, you're betting on everything going right forever — and it won't.

What is a good cap rate for rental property?

There's no number that applies everywhere, and anyone who tells you "you need at least 8%" is selling you a rule of thumb, not a principle. Cap rates move with three things: the market, the asset class, and interest rates.

Rough ranges I've observed across US rental markets:

• 4–6% — expensive coastal metros, strong rent growth expectations, low vacancy
• 6–8% — mid-size cities with steady population growth and reasonable landlord laws
• 8–12% — smaller markets, older housing stock, or neighborhoods where tenant quality and turnover are real risks

A cap rate is fundamentally a risk score in disguise. The higher it goes, the more the market is telling you something is complicated — deferred maintenance, weak job base, tenant turnover, a rent control ordinance on the table. Sometimes that's an opportunity. Sometimes it's an accurate warning.

When interest rates climbed and borrowing got expensive, cap rates didn't rise to match, at least not right away. Sellers held their price expectations while buyers recalculated. That standoff froze a lot of transactions. It also created room for cash buyers who didn't care what a lender thought.

So the honest answer to "what's a good cap rate" is another question: good compared to what? Compared to a bond with zero tenants and zero toilets? Compared to other properties you're actually choosing between? That's the comparison that matters.

How the calculation shifts by property type

The formula stays the same. The inputs change, sometimes dramatically.

Standard long-term rentals

Straightforward: 12-month leases, predictable rent, vacancy around 5%. This is where the basic formula works cleanest.

Short-term and vacation rentals

Here the calculation gets messy, and I'd argue many investors underestimate it. Gross revenue looks spectacular on a platform dashboard. What that dashboard doesn't show you:

• Platform commissions, usually 3–15% depending on the booking channel
• Cleaning fees you pay out but often can't fully charge back
• Furnishing and replacement costs — furniture wears out far faster under weekly turnover
• Utilities, internet, supplies, and higher insurance premiums
• Seasonality: an annual cap rate built on peak-season rates is fiction

A property showing 150% of long-term market rent can easily net out below a plain vanilla lease once you subtract all of that. I've watched two investors buy in the same building on the same weekend; the short-term one cleared less profit after a year, with three times the work.

Commercial properties

Commercial deals — retail, office, small industrial — often use triple-net leases where the tenant pays taxes, insurance and maintenance. That strips most operating expenses out of the NOI calculation, which makes the cap rate cleaner but also more sensitive to tenant credit quality. A 7% cap rate with a national tenant on a ten-year lease and a 7% cap rate with a local business on a handshake are not the same investment, even though the arithmetic looks identical.

Tools, spreadsheets, and the mistakes calculators hide

You can find a cap rate calculator on almost any real estate site. Most of them ask for three inputs: purchase price, gross rent, and total expenses. Type the numbers, get a percentage.

The problem isn't the tool. It's what happens before you type.

I built my own spreadsheet after the third time an online calculator gave me a number that didn't match my bank account at year end. Mine has separate columns for every expense category, a vacancy line I can't accidentally zero out, and a CapEx field that auto-fills with a percentage of gross rent. It's not elegant. It's accurate, which is the point.

If you'd rather use something off the shelf, that's fine — just check what the calculator assumes. Does it include vacancy? Does it ask about management, or does it silently assume you'll do it yourself forever? Does CapEx exist anywhere in its logic? If the answer to those questions is no, you're getting a marketing number, not an investment number.

Three mistakes I made, so you don't have to

1. Using the seller's pro-forma rent instead of market rent. Their number described a tenant who moved out two months before the listing went live.
2. Ignoring the age of major systems. The cap rate looked fine. The furnace was 22 years old.
3. Treating a high cap rate as automatically good. My worst-performing property had the highest cap rate of anything I've owned. It also had the highest turnover, the most repair calls, and a tenant who paid late every single month for a year.

Cap rate tells you what a property produces relative to its price. It says nothing about how much of your time it will consume, and that has a cost whether or not it shows up in a spreadsheet.

Run the conservative version. Use real market rents. Reserve for the roof before it leaks. The number you end up with will be smaller and less exciting than the one the listing promised — and it will be the one that's actually true. Which is the only kind of number worth building a portfolio on.