About the Operating Expense Ratio Calculator
The operating expense ratio (OER) is the share of a property’s income consumed by the costs of running it — property taxes, insurance, repairs and maintenance, management, utilities, payroll and similar expenses. A building that collects $234,000 and spends $88,000 to operate has an OER of about 37.6%. The rest is net operating income (NOI), the money available for debt service and returns.
Enter gross potential rent, a vacancy and credit-loss allowance, other income such as parking or laundry, and each expense line. The calculator returns the OER, total operating expenses, effective gross income, NOI, NOI margin and expense per unit, with a breakdown chart so you can see which costs dominate. You can measure the ratio against effective gross income (the usual underwriting convention) or gross potential income.
Investors use the OER to screen listings with suspiciously low expenses, compare a building with similar properties, and track cost control over time. Mortgage payments, depreciation, income taxes and capital improvements are not operating expenses, so leave them out.
With the default inputs, the operating expense ratio is 37.61%. Change any value above to recalculate instantly.
How to use the operating expense ratio calculator
- 1Enter yearly gross potential rent and a vacancy and credit-loss percentage.
- 2Add other income such as parking, laundry or fees.
- 3Enter each annual operating expense, leaving out mortgage payments and depreciation.
- 4Enter the number of units for a per-unit cost.
- 5Read the OER and compare it with similar properties in your market.
Formula and method
The operating expense ratio divides total annual operating expenses by the property’s income. Most underwriters use effective gross income — gross potential rent minus vacancy and credit loss, plus other income — because that is the income the property actually collects. Some analysts divide by gross potential income instead, which gives a lower ratio, so always state which basis you use when comparing properties.
Operating expenses are the recurring costs of running the property: taxes, insurance, repairs, management, owner-paid utilities, payroll and administration. Debt service, depreciation, income taxes and capital expenditures are excluded. On an EGI basis the NOI margin is simply 100% minus the OER.
- OER
- Operating expense ratio
- EGI
- Effective gross income
- NOI
- Net operating income
Worked examples
20-unit apartment building
Gross rent of $240,000 less 5% vacancy plus $6,000 of other income gives EGI of $234,000. Expenses total $88,000, so the OER is 37.6% and NOI is $146,000 — a 62.4% margin and $4,400 of operating cost per unit.
Same building measured against gross potential income
Dividing $88,000 of expenses by gross potential income of $246,000 (before vacancy) gives a lower OER of 35.8%. NOI does not change; only the ratio’s denominator does, which is why the basis must match when comparing deals.
Fourplex with higher relative costs
EGI is $57,600 × 94% + $1,200 = $55,344. Expenses of $23,500 give an OER of 42.5% and NOI of $31,844; small buildings often run higher ratios because fixed costs are spread over fewer units.
Frequently asked questions
What is the operating expense ratio in real estate?+
The operating expense ratio is a property’s annual operating expenses divided by its income, usually effective gross income. It shows what share of collected income is spent running the property before debt service.
What is a good operating expense ratio?+
Many apartment properties run between roughly 35% and 50% of effective gross income, but the right level depends on age, location, who pays utilities and property type. Compare with similar buildings in the same market rather than a single benchmark.
Is the mortgage included in operating expenses?+
No. Mortgage principal and interest are financing costs, not operating expenses. Depreciation, income taxes and capital improvements are also excluded, so the OER measures operating efficiency regardless of how the property is financed.
What is the difference between OER and the 50% rule?+
The 50% rule is a rough screening assumption that operating expenses will be about half of gross rent. The OER is the actual measured ratio from a property’s numbers, which may be well above or below 50%.
How does OER relate to NOI?+
On an effective gross income basis, the NOI margin equals 100% minus the OER. A property with a 38% OER keeps 62% of its income as net operating income.
Results are estimates for educational purposes and are not financial advice. Rates, fees and terms vary — confirm with your lender or a licensed advisor before making decisions.