Operating expense ratio (OER): what's a good one for a rental? (2026)

What the operating expense ratio measures

The operating expense ratio is the share of a property's income that gets eaten by the cost of running it:

Effective gross income(EGI) is all the money the property actually brings in: gross potential rent, plus any other income like laundry or parking, minus vacancy and collection loss. It's the top line after you've been honest about empty units — not the rent roll's dream number. Operating expenses are what it costs to keep the property running and rentable this year — taxes, insurance, management, repairs, utilities the owner pays, and so on. Divide one by the other and you get a percentage. An OER of 45% means 45 cents of every effective rent dollar goes to running costs, and 55 cents survives as net operating income. Lower is more efficient; higher means the property works harder to keep less.

That last point is why OER matters more than it looks. NOI, cap rate, and — for anything a bank underwrites on its economics — value all sit downstream of this one ratio. Miss it and every number built on top of it is wrong in the same direction.

What counts as an operating expense — and what doesn't

The ratio is only as honest as the line items you feed it, and the classification is where most people go wrong. An operating expense is a recurring cost of running the property that any owner would face regardless of how they financed it. That includes:

• Property taxes and insurance
• Property management (even if you self-manage — more below)
• Repairs and maintenance
• Utilities the owner pays (water/sewer, trash, common-area electric)
• HOA dues, landscaping, snow removal, pest control
• Licensing, turnover/advertising, and property-level accounting or legal
• Replacement reserves for big-ticket items (by appraisal convention)

Four costs are not operating expenses, and folding any of them in wrecks the ratio:

• The mortgage. Principal and interest are financing, not operations. Debt service lives below NOI, so it never touches the OER.
• Depreciation. A paper deduction on your tax return, not a cash cost of running the building.
• Capital expenditures. A new roof or a full HVAC replacement is a capital item, not an operating one — though a reserve that sets money aside for it is a legitimate operating line. Book the reserve, not the lumpy replacement.
• Your income taxes. Personal to you, not to the property.

One more trap: vacancy is not an operating expense. It's a deduction from gross rent that you take to reach effective gross income — the denominator — so it's already accounted for. Investors who list vacancy up in the expense column are double-counting it and inflating the ratio. If you want to pressure-test the assumption that drives that denominator, the vacancy rate calculator derives it from turnover instead of guessing 5%.

A worked example: the $250K duplex

Take a $250,000 duplex, two units at $1,250/month, so $30,000 of gross potential rent a year. Assume 6% vacancy and collection loss, which knocks $1,800 off the top and leaves $28,200 of effective gross income. Here are the operating expenses, line by line:

So the ratio is $11,156 ÷ $28,200 ≈ 40%, and NOI is $28,200 − $11,156 = $17,044, a 6.8% cap rate on the $250,000 price. But notice what's missing: reserves. Add a modest $1,700 replacement reserve — the appraiser always does — and operating expenses climb to $12,856, the OER rises to about 46%, and NOI falls to $15,344, a 6.1% cap rate. That single decision, whether to book reserves, is worth six points of OER and 0.7 points of cap rate on the very same building. It's the classic reserves-and-CapEx question, and it's the difference between a ratio that flatters the deal and one that tells the truth.

What's a good OER? Honest 2026 benchmarks

There is no single right answer, because the ratio depends heavily on the age of the building, who pays the utilities, and how punishing the local tax bill is. As a working set of 2026 bands, measured on effective gross income and excluding debt service:

Two cautions before you use these. First, a high OER isn't automatically a bad deal — a building can run at 55% and still be a strong buy if the rents are high enough that the remaining 45% produces plenty of NOI. OER measures efficiency, not profitability; pair it with cash flow and cap rate before you judge. Second, the bands only compare fairly across properties with the same utility and tax structure. An all-bills-paid building will always post a higher OER than an identical one where tenants pay their own power — that's a difference in who holds the expense, not in how well the property is run.

OER and the 50% rule are the same idea

If the ratio feels familiar, it should: the 50% rule is just the OER done on a napkin. The rule says operating costs run about half of gross rent — but the version investors actually quote bundles vacancy and reserves into that "half" and measures against gross rent rather than effective income. Line the two up on our duplex and they nearly touch. Operating expenses ($11,156) plus vacancy ($1,800) plus reserves ($1,700) come to $14,656 — about 49% of the $30,000 gross rent, almost exactly what the 50% rule predicts.

The difference is precision and denominator. The 50% rule is a five-second screen against gross rent that lets you triage a listing before you've gathered a single real number. The OER is the measured metric against effective income that you compute once you have the actuals — the version that survives a lender's or an appraiser's review. Use the rule to decide whether a deal is worth an hour; use the OER when you sit down to underwrite it.

From OER to value: why the ratio moves the price

Here's the part that turns OER from a trivia number into a money number. Value on any income property a bank underwrites runs through NOI, and NOI is just effective income times one minus the OER:

Because value is a multiple of NOI, and NOI moves one-for-one with the OER, a small error in the ratio levers into a large error in the price. Underwrite our duplex at a rosy 35% OER — the number you get by lowballing management and skipping reserves — and NOI reads $28,200 × 0.65 = $18,330. Run it honestly at the ~46%we built line by line, and NOI is $15,344. At a 6.5% market cap rate, that's the difference between a $282,000 valuation and a $236,000 one — about $46,000 of value riding on an eleven-point assumption about operating efficiency. Nobody argues over a $46,000 price cut, but plenty of investors wave through the OER assumption that causes it. The cap rate calculator and the NOI calculator let you watch that swing move as you change the expense lines.

Five ways people get OER wrong

• Putting the mortgage in the numerator.Debt service is financing, not operations. It belongs below NOI. This is the error that turns a 45% property into a "75% OER disaster" that doesn't exist.
• Double-counting vacancy. Vacancy is netted out of income to reach EGI. Listing it again as an expense inflates the ratio and understates NOI.
• Zeroing out management because you self-manage. Your time isn't free, and a future buyer will price in 8–10% for a manager. Leave it in, or your OER is a personal number that doesn't transfer with the property.
• Skipping reserves entirely.An OER with no line for the roof, the furnace, or the parking lot looks great right up until one of them fails. It's the most common way a deal pencils on paper and bleeds in real life.
• Comparing across different utility or tax setups. An all-bills-paid or high-tax property carries a structurally higher OER. Normalize for who pays what before you rank two buildings against each other.

FAQ

The bottom line

The operating expense ratio is the cleanest one-number read on how hard a property has to work to keep what it earns. Compute it honestly — operating expenses over effective gross income, with reserves in and the mortgage, depreciation, capital items, and vacancy out — and it tells you at a glance whether a building runs efficiently, how it stacks up against comparable properties, and exactly how much NOI survives to drive value. Get lazy with the inputs and it becomes a flattering fiction that talks you into overpaying. Anchor it against the 50% rule as a sanity check, and let the TrueCap analyzer carry the operating expenses straight through to NOI, cap rate, cash flow, and DSCR — so the ratio you assume and the verdict you get always come from the same set of numbers. None of this is investment advice; confirm the actual expenses, taxes, and rents on any specific property before you rely on the ratio.