Single-family homes are usually valued by comparing them to similar homes nearby. Apartment buildings are different. Because they are income-producing businesses, their value is driven primarily by the income they generate. Two numbers do most of the work: net operating income (NOI) and the capitalization rate (cap rate).
What Is Net Operating Income?
NOI is the income a property produces after operating expenses, but before debt payments and income taxes. The basic formula is:
NOI = Effective Gross Income − Operating Expenses
Effective gross income starts with the rent the property could collect if every unit were leased, then subtracts vacancy, concessions, and bad debt, and adds other income such as laundry, parking, or pet fees.
Operating expenses include property taxes, insurance, utilities paid by the owner, repairs and maintenance, payroll, property management, and a reserve for future capital needs. Mortgage payments are not an operating expense.
What Is a Cap Rate?
The cap rate expresses the relationship between a property’s NOI and its value:
Cap Rate = NOI ÷ Property Value
Rearranged, it becomes a valuation tool: Value = NOI ÷ Cap Rate. For example, a property producing $100,000 of NOI at a 6% cap rate would be valued at roughly $1,666,667. The same NOI at a 7% cap rate implies about $1,428,571.
Cap rates reflect how the market views risk and growth for a given property type and location. Lower cap rates generally indicate lower perceived risk or stronger growth expectations; higher cap rates suggest the opposite.
Why Small NOI Changes Matter So Much
Because value is NOI divided by the cap rate, every dollar of NOI is multiplied. At a 6% cap rate, increasing NOI by $10,000 per year can add roughly $166,000 of value. That is why value-add investors focus so intensely on raising income and controlling expenses.
Common Mistakes
- Trusting a pro forma. Marketing packages often show projected NOI, not actual NOI. Always rebuild the numbers from the rent roll and trailing twelve-month statements.
- Ignoring tax reassessment. In many areas, property taxes reset after a sale. Using the seller’s current tax bill can overstate NOI.
- Leaving out reserves. Roofs, boilers, and parking lots eventually need replacement. A realistic reserve belongs in the expense line.
- Forgetting management costs. Even if an owner self-manages, a buyer should budget for professional management.
- Comparing cap rates across very different properties. A cap rate on a newer, stabilized building is not directly comparable to one on an older, value-add property.
Putting It Together
NOI tells you what a property earns. The cap rate tells you what the market is willing to pay for those earnings. A disciplined investor starts with an honest NOI, applies a cap rate grounded in comparable sales, and then stress-tests both before deciding what to pay.
That is the same approach we use at Skyline Capital Investments. See how we underwrite.
