Net Operating Income (NOI): Formula, Calculator & Examples
If you only learn one number in real estate investing, make it NOI. Net Operating Income is the foundation of property valuation, loan qualification, and investment analysis. It's the property's profit from operations — before debt service and before taxes — and it determines what a property is worth in the eyes of lenders, appraisers, and buyers.
This guide goes beyond the basic formula with worked examples for different property types, common calculation mistakes, and practical tips for increasing your property's NOI.
The NOI Formula
NOI = Effective Gross Income - Operating Expenses
Where:
- Effective Gross Income = Gross Potential Rent + Other Income - Vacancy & Credit Loss
- Operating Expenses = All costs to run the property (excluding mortgage and CapEx)
Example 1: Single-Family Rental
| Income | Annual |
|---|---|
| Gross potential rent ($1,600/mo) | $19,200 |
| Pet rent ($50/mo) | $600 |
| Late fees | $150 |
| Gross potential income | $19,950 |
| Vacancy allowance (5%) | -$998 |
| Effective gross income | $18,952 |
| Operating Expenses | Annual |
|---|---|
| Property taxes | $3,600 |
| Insurance | $1,200 |
| Property management (10%) | $1,895 |
| Repairs & maintenance | $1,500 |
| Lawn care | $720 |
| Pest control | $240 |
| Total operating expenses | $9,155 |
NOI = $18,952 - $9,155 = $9,797
Operating expense ratio: 48.3% (within the typical 35-50% range for SFR)
Example 2: 8-Unit Apartment Building
| Income | Annual |
|---|---|
| 8 units × $1,100/mo | $105,600 |
| Laundry income | $2,400 |
| Storage unit fees (4 × $75/mo) | $3,600 |
| Gross potential income | $111,600 |
| Vacancy & credit loss (7%) | -$7,812 |
| Effective gross income | $103,788 |
| Operating Expenses | Annual |
|---|---|
| Property taxes | $12,000 |
| Insurance | $4,800 |
| Property management (8%) | $8,303 |
| Repairs & maintenance | $8,000 |
| Water/sewer/trash | $6,000 |
| Common area electric | $1,800 |
| Landscaping | $2,400 |
| Legal & accounting | $1,500 |
| Advertising | $600 |
| Total operating expenses | $45,403 |
NOI = $103,788 - $45,403 = $58,385
Operating expense ratio: 43.7%
At a 7% cap rate, this property is worth: $58,385 / 0.07 = $834,071
Example 3: Small Retail Building
| Income | Annual |
|---|---|
| Base rent (2 tenants, NNN leases) | $72,000 |
| CAM reimbursements | $12,000 |
| Tax reimbursements | $8,000 |
| Insurance reimbursements | $3,000 |
| Gross potential income | $95,000 |
| Vacancy (5% — one tenant has 3 years remaining on lease) | -$4,750 |
| Effective gross income | $90,250 |
| Operating Expenses | Annual |
|---|---|
| Property taxes | $8,000 |
| Insurance | $3,000 |
| CAM expenses | $12,000 |
| Property management (5%) | $4,513 |
| Repairs | $4,000 |
| Total operating expenses | $31,513 |
NOI = $90,250 - $31,513 = $58,737
Note: NNN (triple net) leases pass taxes, insurance, and CAM through to tenants, which is why the reimbursements appear as both income and expense — they largely cancel out. The net effect is a higher NOI margin for the landlord.
The 50% Rule: Quick Screening Only
The "50% rule" says that operating expenses will eat about 50% of gross rent. So if a property rents for $2,000/month ($24,000/year), NOI is approximately $12,000.
This is useful for screening properties quickly on Zillow or in a listing feed. But it's only a rough estimate:
- Newer properties with low maintenance: expenses may be 35-40%
- Older properties or those with owner-paid utilities: expenses may be 55-65%
- NNN commercial leases: expenses may be 15-25% (tenants cover most)
Always calculate actual NOI before making an offer.
NOI and Property Value: The Multiplier Effect
Here's why NOI is so powerful: in the income approach to valuation, every $1 increase in NOI increases property value by $1 divided by the cap rate.
| NOI Increase | Cap Rate | Value Increase |
|---|---|---|
| $1,000 | 5% | $20,000 |
| $1,000 | 7% | $14,286 |
| $1,000 | 10% | $10,000 |
| $5,000 | 6% | $83,333 |
| $10,000 | 7% | $142,857 |
This is the basis of the "value-add" investment strategy: buy a property with below-market NOI, increase it through better management, rent increases, or expense reduction, and the property's value jumps by a multiple of the NOI increase.
Common NOI Calculation Errors
- Including mortgage payments — the most common beginner mistake. NOI is before debt service. Always.
- Forgetting vacancy — even if the property is currently fully occupied, budget for future vacancy (5-10%)
- Omitting management — if you self-manage, include 8-12% anyway. It's a real cost even if you're not writing a check.
- Using pro forma instead of actual — sellers show best-case numbers. Verify with bank statements and tax returns.
- Confusing CapEx with operating expenses — a new roof ($15,000) is CapEx, not an operating expense. Regular patch repairs ($500) are operating expenses.
Related Articles
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- Income Approach to Real Estate Valuation
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