If you have property that you rent out. You have money coming in every month in the form of rents. Some properties, paticularly larger multiunit complexes, may have some additional sources, such as from coin-operated washers and dryers. When you own investment real estate, you should also expect to incur expenses that include your mortgage payment,property taxes, insuance, and maintenance. The interaction of the revenues coming in and the expenses going out is what tells you whether you realize positive operating profit each month.