1. Get the most recent sale price or, in the case of new construction, order an appraisal and get a fair market value.
2. Determine the net operating income for the property (current or projected gross rental income minus current or projected expenses paid by the owner (taxes, insurance, any financing costs, operating costs, etc.).
3. Divide the net operating income by the sale price (or appraised value, if new) to get the CAP rate.
NOI / Price = CAP Rate
In this case, we would need extensive information from you to actually determine the CAP rate. Since youâ€™ve given us nothing, Iâ€™m hoping the above formula is what you actually need.