I'm not an expert, just a contractor from Maryland, but the formula I've seen here and one my associate uses to purchase is: You Multiply ARV by .70, with is 70% of ARV. Then minus repair cost to arrive at the top value you should pay for the property. So in your case it would be .70x450k = 315k. minus example 75k repairs=240k max price to pay for property, leaving a profit of 135k. Witch is 30% of ARV :). Again I'm not an investor but it looks right.