Cap Rate Formula. The formula for Cap Rate is equal to Net Operating Income (NOI) divided by the current market value of the asset. Where: Net operating income is the annual income Annual Income Annual income is the total value of income earned during a fiscal year. Gross annual income refers to all earnings before any deductions are made, and Net operating income (I) ÷sales price (V) = capitalization rate (R) This formula is applied using the net operating income and sale price of each comparable that you’re analyzing. Note in this formula, the reversal of the IRV formula for finding value. Here’s an example: A building sells for $200,000. Its net operating income is $20,000. CAP Rate = Net operating income divided by the price of a property. For example, if you buy a property for $100,000 and the net income is $10,000 a year, the cap rate is 10%. ($10,000/$100,000=10%) The cap rate can be figured out very easily, but the tricky part is knowing how accurate the income numbers are on a particular property.