using flip calculator

[Cindy Berner]

This might sound very basic - I'm trying to use the flip calculator on the site.  When prompted to enter monthly holding costs I have to use a specific loan amount, correct??  I'm not understanding how the calculation will ultimately give me the max offer amount if I'm entering the loan dollar amount.  I'm also going to be obtaining a loan which will include purchase price + rehab estimate costs.  Hopefully, I've explained my question so someone can understand!?