Advice Needed To Present ROI to Private Investor

[Arouna Koroma]

Hello - I'm a real estate broker and investor with 27+ yrs in the industry however it's my first week as a BP Pro account user ;-) 

I have a private investor interested in a 5 unit building I have under contract. The plan is to hold the property for about 18-24 months then convert it to a single family home and resell it on the market. It will carry itself for the most part during hold period and my private investor is willing to assist with any downpayment and renovation costs needed. My question is which analysis calculator should I use to show my investor his ROI?