Question about IBR

Sorry if this is a stupid question, but I'm a little confused when it comes to IBR. Granted, I haven't looked into it very deeply, but it's based on your income from your previous tax return, correct? What concerns me is that if they're simply looking at my income and what I owe on my loan, the repayment offer won't be very good because it will look like I make too much. For clarification, I owe a little over $17,000 in federal loans, and make ~30k a year. If that's all I had to pay for, I'd be fine. But, I also have around $36,000 in private loans (long story) that is drowning me. So basically my question is, how do I get an accurate repayment figure for IBR if they don't take into account my other debt?