http://www.finaid.org/loans/ibr.phtml
The Income-Based Repayment (IBR) plan was proposed as part of the College Cost Reduction and Access Act of 2007 and will become available on July 1, 2009.
Income-based repayment is only available for federal student loans, such as the Stafford, Grad PLUS and consolidation loans. It is not available for Parent PLUS loans or for consolidation loans that include Parent PLUS loans. (IBR is not available for Perkins loans, but it is available for consolidation loans that include Perkins loans.) It is also not available for private student loans.
Income-based repayment is similar to income-contingent repayment. Both cap the monthly payments at a percentage of your discretionary income, albeit with different percentages and different definitions of discretionary income. Income-based repayment caps monthly payments at 15% of your monthly discretionary income, where discretionary income is the difference between adjusted gross income (AGI) and 150% of the federal poverty line that corresponds to your family size and the state in which you reside. There is no minimum monthly payment.