How to Calculate private money loans on a rehab in Excel

[Jonathan Johnson]

Hello BP!

I'm trying to figure out how to analyse rehab costs and one of them is using private money.

If I can buy a house for W amount of dollars, and it needs X amount of repairs, how much will a Y% private loan for repairs(Y) cost over Z amount of months? 

Basically how do I know the cost taking out a higher percent loan for repairs and then refinancing later back into a regular loan?