Excel Formula Question for ROI Calculation

[Brandon Powell]

I have hit a wall trying to build a relatively simple math formula to assist in our fix and flip business. We would like to be able to quickly compare deals based on a target ROI of 40%.

I am attempting to flip a formula around and solve for the Offer Amount given a set ROI Goal of 40%.

ROI = Net Profit / (Offer Amount + Buying Costs + Holding Costs) / (Rehab Months / 12)

**Note:  Offer Amount + Buying Costs + Holding Costs = Total Investment

I was able to get he formula correct as long as the Rehab Months are not included...see below:

Offer Amount = (Net Profit / 0.4) - (Buying Costs + Holding Costs)

I just can't seem to figure out how the formula changes to account for the Rehab Months. 

Anybody out there good with flipping formulas around???