The math behind a "deal"

[Seth Willis]

Hello BP,

I am fairly new to RE investing and was wanting to know some of the back end math to it. How much do you pay to remodel, how do you figure if the house is cash flow positive for a buy and hold situation. What are the formulas behind these. I have found multiple "deals" in my area but I'm starting to think I could be doing my math wrong and I want real numbers before I start my real estate future. 

Thank you.