Technically the cap rate calculation is used to determine value. So you would determine what the “cap rates” of recently nearby sold properties were, and then use that number to establish what a good purchase price would be for a property you are looking to purchase.
I have both my simple cap rate calculator, as well as my full investment calculator, accessible in my free course on understanding real estate investment returns.
Your net operating income is your total revenue for the property, less your total expenses. It’s also commonly referred to “Cash Flow”, or the (hopeful) cash you have in hand at the end of the year.
The type of lease you have with tenants will impact your cap rate. The lease will drive your overall expenses for the property, which is a factor of NOI.
When you are looking at purchasing a rental property, you will want to calculate as much information as possible related to the income and expenses. Then think about how your expenses may change over time, as well as any increase in rents.