How to determin an offer price?

[John Speener]

So I am a new investor that doesn't have problems finding great deals. The question that I need help with is how do you determine what is a solid offer on their house that they are about to lose? So far what I have come up with is to work backwards from what their house is worth. For instance if their house is $600,000 and you know that they still owe $90,000 on the mortgage, another $50,000 in taxes, it needs $150,000 in repairs, plus $16,000 in real estate fees, and a few grand to carry it for 4 to 6 month waiting for it to sale. So what I'm thinking is to back out those prices for the value of the house then you are left with profit. How much of that profit should be offered to the home owner? Is there a percentage that works for everyone? Or maybe a great program that could calculate what the offer should be? I would very much appreciate any information or help that I can get in this area.