NOI can be calculated as:

Net Operating Income (NOI) is a key metric used in real estate to assess the profitability of an income-producing property. It is calculated as the total revenue generated by the property minus the operating expenses associated with running and maintaining that property.

In more detail, the total revenue typically includes rents collected from tenants and any additional income streams such as fees for amenities or services. Operating expenses encompass costs necessary to operate the property, including property management fees, maintenance, utilities, property insurance, and property taxes. By subtracting these expenses from the total revenue, investors and property managers can determine the property's profitability before financing costs and taxes are taken into account.

Thus, the correct answer accurately reflects the formula for calculating NOI, highlighting the importance of understanding income and expenses in real estate management.