To calculate the value of an apartment building, you need to know two numbers: the property's net operating income (NOI) and the local market capitalization rate (Market CAP). Once you have those two numbers, you will use the following formula (NOI/Market CAP= Value). For example, let's say the NOI is $300,000, and in the particular submarket where the property is located, the market CAP is 6.5%. Here's how that would look> $300,000/0.065=$4.6MM.